@article{dunham_endeve_mezzacappa_blondin_buffaloe_holley-bockelmann_2024, title={A Parametric Study of the SASI Comparing General Relativistic and Nonrelativistic Treatments}, volume={964}, ISSN={["1538-4357"]}, url={https://doi.org/10.3847/1538-4357/ad206c}, DOI={10.3847/1538-4357/ad206c}, abstractNote={
 We present numerical results from a parameter study of the standing accretion shock instability (SASI), investigating the impact of general relativity (GR) on the dynamics. Using GR hydrodynamics with GR gravity, and nonrelativistic (NR) hydrodynamics with Newtonian gravity, in an idealized model setting, we vary the initial radius of the shock, and by varying its mass and radius in concert, the proto-neutron star compactness. We investigate four compactnesses expected in a post-bounce core-collapse supernova (CCSN). We find that GR leads to a longer SASI oscillation period, with ratios between the GR and NR cases as large as 1.29 for the highest-compactness suite. We also find that GR leads to a slower SASI growth rate, with ratios between the GR and NR cases as low as 0.47 for the highest-compactness suite. We discuss implications of our results for CCSN simulations.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Dunham, Samuel J. and Endeve, Eirik and Mezzacappa, Anthony and Blondin, John M. and Buffaloe, Jesse and Holley-Bockelmann, Kelly}, year={2024}, month={Mar} }
 @article{mezzacappa_marronetti_landfield_lentz_murphy_hix_harris_bruenn_blondin_messer_et al._2023, title={Core collapse supernova gravitational wave emission for progenitors of 9.6, 15, and 25M(?)}, volume={107}, ISSN={["2470-0029"]}, url={https://doi.org/10.1103/PhysRevD.107.043008}, DOI={10.1103/PhysRevD.107.043008}, abstractNote={We present gravitational wave emission predictions based on three core collapse supernova simulations corresponding to three different progenitor masses. The masses span a large range, between 9.6 and 25 Solar masses, are all initially non-rotating, and are of two metallicities: zero and Solar. We compute both the temporal evolution of the gravitational wave strains for both the plus and the cross polarizations, as well as their spectral decomposition and characteristic strains.}, number={4}, journal={PHYSICAL REVIEW D}, author={Mezzacappa, Anthony and Marronetti, Pedro and Landfield, Ryan E. and Lentz, Eric J. and Murphy, R. Daniel and Hix, W. Raphael and Harris, J. Austin and Bruenn, Stephen W. and Blondin, John M. and Messer, O. E. Bronson and et al.}, year={2023}, month={Feb} }
 @article{ramachandran_oskinova_hamann_sander_todt_pauli_shenar_torrejon_postnov_blondin_et al._2022, title={Phase-resolved spectroscopic analysis of the eclipsing black hole X-ray binary M33 X-7: System properties, accretion, and evolution}, volume={667}, ISSN={["1432-0746"]}, DOI={10.1051/0004-6361/202243683}, abstractNote={M33X-7 is the only known eclipsing black hole high mass X-ray binary. The system is reported to contain a very massive O supergiant donor and a massive black hole in a short orbit. The high X-ray luminosity and its location in the metal-poor galaxy M33 make it a unique laboratory for studying the winds of metal-poor donor stars with black hole companions and it helps us to understand the potential progenitors of black hole mergers. Using phase-resolved simultaneous HST - and XMM-Newton -observations, we traced the interaction of the stellar wind with the black hole. We observed a strong Hatchett-McCray e ff ect in M33X-7 for the full range of wind velocities. Our comprehensive spectroscopic investigation of the donor star (X-ray + UV + optical) yields new stellar and wind parameters for the system that di ff er significantly from previous estimates. In particular, the masses of the components are considerably reduced to ≈ 38 M (cid:12) for the O-star donor and ≈ 11 . 4 M (cid:12) for the black hole. The O giant is overfilling its Roche lobe and shows surface He enrichment. The donor shows a densely clumped wind with a mass-loss rate that matches theoretical predictions. An extended ionization zone is even present during the eclipse due to scattered X-ray photons. The X-ray ionization zone extends close to the photosphere of the donor during inferior conjunction. We investigated the wind-driving contributions from di ff erent ions and the changes in the ionization structure due to X-ray illumination. Toward the black hole, the wind is strongly quenched due to strong X-ray illumination. For this system, the standard wind-fed accretion scenario alone cannot explain the observed X-ray luminosity, pointing toward an additional mass overflow, which is in line with our acceleration calculations. The X-ray photoionization creates an He ii emission region around the system emitting ∼ 10 47 phs − 1 . We computed binary evolutionary tracks for the system using MESA. Currently, the system is transitioning toward an unstable mass transfer phase, possibly resulting in a common envelope of the black hole and the O-star donor. Since the mass ratio is q (cid:38) 3.3 and the period is short, the system is unlikely to survive the common envelope, but will rather merge.}, journal={ASTRONOMY & ASTROPHYSICS}, author={Ramachandran, V. and Oskinova, L. M. and Hamann, W. -r. and Sander, A. A. C. and Todt, H. and Pauli, D. and Shenar, T. and Torrejon, J. M. and Postnov, K. A. and Blondin, J. M. and et al.}, year={2022}, month={Nov} }
 @article{stone_johnson_blondin_watson_borkowski_frohlich_seitenzahl_reynolds_2021, title={Type Ia Supernova Models: Asymmetric Remnants and Supernova Remnant G1.9+0.3}, volume={923}, ISSN={["1538-4357"]}, url={https://doi.org/10.3847/1538-4357/ac300f}, DOI={10.3847/1538-4357/ac300f}, abstractNote={The youngest Galactic supernova remnant, G1.9+0.3, probably the result of a Type Ia supernova, shows surprising anomalies in the distribution of its ejecta in space and velocity. In particular, high-velocity shocked iron is seen in several locations far from the remnant center, in some cases beyond prominent silicon and sulfur emission. These asymmetries strongly suggest a highly asymmetric explosion. We present high-resolution hydrodynamic simulations in two and three dimensions of the evolution from ages of 100 s to hundreds of years of two asymmetric Type Ia models, expanding into a uniform medium. At the age of G1.9+0.3 (about 100 yr), our 2D model shows almost no iron shocked to become visible in X-rays. Only in a much higher-density environment could significant iron be shocked, at which time the model's expansion speed is completely inconsistent with the observations of G1.9+0.3. Our 3D model, evolving the most asymmetric of a suite of Type Ia supernova models from Seitenzahl et al. (2013), shows some features resembling G1.9+0.3. We characterize its evolution with images of composition in three classes: C and O, intermediate-mass elements (IMEs), and iron-group elements (IGEs). From ages of 13 to 1800 yr, we follow the evolution of the highly asymmetric initial remnant as the explosion asymmetries decrease in relative strength, to be replaced by asymmetries due to evolutionary hydrodynamic instabilities. At an age of about 100 yr, our 3D model has comparable shocked masses of C+O, IMEs, and IGEs, with about 0.03 M ⊙ each. Evolutionary changes appear to be rapid enough that continued monitoring with the Chandra X-ray Observatory may show significant variations.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, publisher={American Astronomical Society}, author={Stone, Alice G. and Johnson, Heather T. and Blondin, John M. and Watson, Richard A. and Borkowski, Kazimierz J. and Frohlich, Carla and Seitenzahl, Ivo R. and Reynolds, Stephen P.}, year={2021}, month={Dec} }
 @article{bruenn_blondin_hix_lentz_messer_mezzacappa_endeve_harris_marronetti_budiardja_et al._2020, title={Chimera: A Massively Parallel Code for Core-collapse Supernova Simulations}, url={https://doi.org/10.3847/1538-4365/ab7aff}, DOI={10.3847/1538-4365/ab7aff}, abstractNote={We provide a detailed description of the Chimera code, a code developed to model core collapse supernovae (CCSNe) in multiple spatial dimensions. The CCSN explosion mechanism remains the subject of intense research. Progress to date demonstrates that it involves a complex interplay of neutrino production, transport, and interaction in the stellar core, three-dimensional stellar core fluid dynamics and its associated instabilities, nuclear burning, and the fundamental physics of the neutrino–stellar core weak interactions and the equations of state of all stellar core constituents—particularly, the nuclear equation of state associated with core nucleons, both free and bound in nuclei. Chimera, by incorporating detailed neutrino transport, realistic neutrino–matter interactions, three-dimensional hydrodynamics, realistic nuclear, leptonic, and photonic equations of state, and a nuclear reaction network, along with other refinements, can be used to study the role of neutrino radiation, hydrodynamic instabilities, and a variety of input physics in the explosion mechanism itself. It can also be used to compute observables such as neutrino signatures, gravitational radiation, and the products of nucleosynthesis associated with CCSNe. The code contains modules for neutrino transport, multidimensional compressible hydrodynamics, nuclear reactions, a variety of neutrino interactions, equations of state, and modules to provide data for post-processing observables such as the products of nucleosynthesis, and gravitational radiation. Chimera is an evolving code, being updated periodically with improved input physics and numerical refinements. We detail here the current version of the code, from which future improvements will stem, which can in turn be described as needed in future publications.}, journal={The Astrophysical Journal Supplement Series}, author={Bruenn, Stephen W. and Blondin, John M. and Hix, W. Raphael and Lentz, Eric J. and Messer, O. E. Bronson and Mezzacappa, Anthony and Endeve, Eirik and Harris, J. Austin and Marronetti, Pedro and Budiardja, Reuben D. and et al.}, year={2020}, month={May} }
 @article{mezzacappa_marronetti_landfield_lentz_yakunin_bruenn_hix_messer_endeve_blondin_et al._2020, title={Gravitational-wave signal of a core-collapse supernova explosion of a 15 M⊙ star}, url={https://doi.org/10.1103/PhysRevD.102.023027}, DOI={10.1103/PhysRevD.102.023027}, abstractNote={We report on the gravitational-wave signal computed in the context of a three-dimensional simulation of a core-collapse supernova explosion of a $15\text{ }{M}_{\ensuremath{\bigodot}}$ star. The simulation was performed with our neutrino hydrodynamics code chimera. We detail the gravitational wave strains as a function of time, for both polarizations, and discuss their physical origins. We also present the corresponding spectral signatures. Gravitational wave emission in our model has two key features: low-frequency emission (less than 200 Hz) emanates from the gain layer as a result of neutrino-driven convection and the standing accretion shock instability (SASI), and high-frequency emission (greater than 600 Hz) emanates from the proto--neutron star due to Ledoux convection within it. The high-frequency emission dominates the gravitational wave emission in our model and emanates largely from the convective layer itself, not from the convectively stable layer above it, due to convective overshoot. Moreover, the low-frequency emission emanates from the gain layer itself, not from the proto--neutron star, due to accretion onto it. We provide evidence of the SASI in our model and demonstrate that the peak of our low-frequency gravitational wave emission spectrum corresponds to it. Given its origin in the gain layer, we classify the SASI emission in our model as p-mode emission and assign a purely acoustic origin, not a vortical--acoustic origin, to it. We compare the results of our three-dimensional model analysis with those obtained from the model's two-dimensional counterpart and find a significant reduction in the strain amplitudes in the former case, as well as significant reductions in all related quantities. Our dominant proto--neutron star gravitational wave emission is not well characterized by emission from surface g modes, complicating the relationship between peak frequencies observed and the mass and radius of the proto--neutron star expressed by analytic estimates under the assumption of surface g-mode emission. We present our frequency normalized characteristic strain along with the sensitivity curves of current- and next-generation gravitational wave detectors. This simple analysis indicates that the spectrum of gravitational wave emission between approximately 20 Hz and approximately 1 kHz, stemming from neutrino-driven convection, the SASI, accretion onto the proto--neutron star, and proto--neutron star convection, will be accessible for a Galactic event.}, journal={Physical Review D}, author={Mezzacappa, Anthony and Marronetti, Pedro and Landfield, Ryan E. and Lentz, Eric J. and Yakunin, Konstantin N. and Bruenn, Stephen W. and Hix, W. Raphael and Messer, O. E. Bronson and Endeve, Eirik and Blondin, John M. and et al.}, year={2020}, month={Jul} }
 @article{anguiano_lewis_corcoran_washington_majewski_prieto_mazzola_badenes_stassun_blondin_2020, title={White Dwarfs in Close Binaries: A Systematic Search for Mass-transfer Systems and Supernova Ia Progenitors in the APOGEE Survey}, url={https://doi.org/10.3847/2515-5172/abac04}, DOI={10.3847/2515-5172/abac04}, abstractNote={We have created a new and unique database, the APOGEE–Galaxy Evolution Explorer (GALEX)–Gaia catalog, to study white dwarfs in close binaries, and, in particular, to: (1) create a minimally biased sample of white dwarf-main sequence (WDMS) systems derived from the combination of GALEX, Gaia, and the dual hemisphere, multi-epoch, high-resolution, infrared APOGEE-1 and -2 spectroscopic surveys, and (2) exploit this catalog to vastly increase the number of well-characterized WDMS systems having derived dynamical parameters (e.g., masses, separation, orbital periods, etc.) as well as precision multi-element chemical compositions by exploiting the high resolution, multi-epoch data from APOGEE. This catalog will significantly further our understanding of compact binary evolution.}, journal={Research Notes of the AAS}, author={Anguiano, Borja and Lewis, Hannah M. and Corcoran, Kyle A. and Washington, Jasmin and Majewski, Steven R. and Prieto, Carlos Allende and Mazzola, Christine N. and Badenes, Carles and Stassun, Keivan and Blondin, John}, year={2020}, month={Aug} }
 @article{slane_lovchinsky_kolb_snowden_temim_blondin_bocchino_miceli_chevalier_hughes_et al._2018, title={Investigating the Structure of Vela X}, volume={865}, ISSN={["1538-4357"]}, url={https://doi.org/10.3847/1538-4357/aada12}, DOI={10.3847/1538-4357/aada12}, abstractNote={Abstract}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Slane, P. and Lovchinsky, I and Kolb, C. and Snowden, S. L. and Temim, T. and Blondin, J. and Bocchino, F. and Miceli, M. and Chevalier, R. A. and Hughes, J. P. and et al.}, year={2018}, month={Oct} }
 @article{kolb_blondin_slane_temim_2017, title={Evolution of a Pulsar Wind Nebula within a Composite Supernova Remnant}, volume={844}, url={https://doi.org/10.3847/1538-4357/aa75ce}, DOI={10.3847/1538-4357/aa75ce}, abstractNote={The interaction between a pulsar wind nebula (PWN) and its host supernova remnant (SNR) can produce a vast array of observable structures. Asymmetry present within these structures derives from the complexity of the composite system, where many factors take turns playing a dominating hand throughout the stages of composite SNR evolution. Of particular interest are systems characterized by blastwave expansion within a nonuniform interstellar medium (ISM), which contain an active pulsar having a substantial “kick” velocity (upward of 300 km s − 1 ), because these systems tend to produce complex morphologies. We present a numerical model that employs these and several other factors in an effort to generate asymmetry similar to that seen in various X-ray and radio observations. We find that the main parameters driving structure are ISM uniformity and total pulsar spin-down energy, with secondary contributions from factors such as pulsar trajectory and initial spin-down luminosity. We also investigate the dynamics behind PWN “tails,” which may form to link active pulsars to a crushed, relic nebula as the reverse shock passes. We find that the directions of such tails are not good indicators of pulsar motion, but direction does reveal the flow of ejecta created by the passage of a reverse shock.}, number={1}, journal={The Astrophysical Journal}, publisher={American Astronomical Society}, author={Kolb, Christopher and Blondin, John and Slane, Patrick and Temim, Tea}, year={2017}, month={Jul}, pages={1} }
 @article{blondin_chevalier_2017, title={Pulsar Wind Bubble Blowout from a Supernova}, volume={845}, ISSN={["1538-4357"]}, url={https://doi.org/10.3847/1538-4357/aa8267}, DOI={10.3847/1538-4357/aa8267}, abstractNote={Abstract}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Blondin, John M. and Chevalier, Roger A.}, year={2017}, month={Aug} }
 @article{blondin_gipson_harris_mezzacappa_2017, title={The Standing Accretion Shock Instability: Enhanced Growth in Rotating Progenitors}, volume={835}, ISSN={1538-4357}, url={http://dx.doi.org/10.3847/1538-4357/835/2/170}, DOI={10.3847/1538-4357/835/2/170}, abstractNote={We investigate the effect of progenitor rotation on the standing accretion shock instability (SASI) using two- and three-dimensional hydrodynamic simulations. We find that the growth rate of the SASI is a near-linearly increasing function of the specific angular momentum in the accreting gas. Both the growth rate and the angular frequency in the two-dimensional model with cylindrical geometry agree well with previous linear stability analyses. When excited by very small random perturbations, a one-armed spiral mode dominates the small rotation rates predicted by current stellar evolution models, while progressively higher-order modes are seen as the specific angular momentum increases.}, number={2}, journal={The Astrophysical Journal}, publisher={American Astronomical Society}, author={Blondin, John M. and Gipson, Emily and Harris, Sawyer and Mezzacappa, Anthony}, year={2017}, month={Jan}, pages={170} }
 @article{williams_coyle_yamaguchi_depasquale_seitenzahl_hewitt_blondin_borkowski_ghavamian_petre_et al._2017, title={The Three-dimensional Expansion of the Ejecta from Tycho's Supernova Remnant}, volume={842}, ISSN={["1538-4357"]}, url={https://doi.org/10.3847/1538-4357/aa7384}, DOI={10.3847/1538-4357/aa7384}, abstractNote={Abstract}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Williams, Brian J. and Coyle, Nina M. and Yamaguchi, Hiroya and Depasquale, Joseph and Seitenzahl, Ivo R. and Hewitt, John W. and Blondin, John M. and Borkowski, Kazimierz J. and Ghavamian, Parviz and Petre, Robert and et al.}, year={2017}, month={Jun} }
 @article{williams_chomiuk_hewitt_blondin_borkowski_ghavamian_petre_reynolds_2016, title={AN X-RAY AND RADIO STUDY OF THE VARYING EXPANSION VELOCITIES IN TYCHO’S SUPERNOVA REMNANT}, volume={823}, ISSN={2041-8213}, url={http://dx.doi.org/10.3847/2041-8205/823/2/L32}, DOI={10.3847/2041-8205/823/2/l32}, abstractNote={ABSTRACT}, number={2}, journal={The Astrophysical Journal}, publisher={American Astronomical Society}, author={Williams, Brian J. and Chomiuk, Laura and Hewitt, John W. and Blondin, John M. and Borkowski, Kazimierz J. and Ghavamian, Parviz and Petre, Robert and Reynolds, Stephen P.}, year={2016}, month={May}, pages={L32} }
 @article{hix_lentz_bruenn_mezzacappa_messer_endeve_blondin_harris_marronetti_yakunin_et al._2016, title={THE MULTI-DIMENSIONAL CHARACTER OF CORE-COLLAPSE SUPERNOVAE}, volume={47}, ISSN={["1509-5770"]}, DOI={10.5506/aphyspolb.47.645}, abstractNote={Core-collapse supernovae, the culmination of massive stellar evolution, are spectacular astronomical events and the principle actors in the story of our elemental origins. Our understanding of these events, while still incomplete, centers around a neutrino-driven central engine that is highly hydrodynamically unstable. Increasingly sophisticated simulations reveal a shock that stalls for hundreds of milliseconds before reviving. Though brought back to life by neutrino heating, the development of the supernova explosion is inextricably linked to multi-dimensional fluid flows. In this paper, the outcomes of three-dimensional simulations that include sophisticated nuclear physics and spectral neutrino transport are juxtaposed to learn about the nature of the three dimensional fluid flow that shapes the explosion. Comparison is also made between the results of simulations in spherical symmetry from several groups, to give ourselves confidence in the understanding derived from this juxtaposition.}, number={3}, journal={ACTA PHYSICA POLONICA B}, author={Hix, W. R. and Lentz, E. J. and Bruenn, S. W. and Mezzacappa, A. and Messer, O. E. B. and Endeve, E. and Blondin, J. M. and Harris, J. A. and Marronetti, P. and Yakunin, K. N. and et al.}, year={2016}, month={Mar}, pages={645–657} }
 @article{bruenn_lentz_hix_mezzacappa_harris_messer_endeve_blondin_chertkow_lingerfelt_et al._2016, title={The Development of Explosions in Axisymmetricab Initio core-collapse Supernova Simulations of 12–25 M⊙ Stars}, volume={818}, ISSN={1538-4357}, url={http://dx.doi.org/10.3847/0004-637X/818/2/123}, DOI={10.3847/0004-637x/818/2/123}, abstractNote={ABSTRACT}, number={2}, journal={The Astrophysical Journal}, publisher={American Astronomical Society}, author={Bruenn, Stephen W. and Lentz, Eric J. and Hix, W. Raphael and Mezzacappa, Anthony and Harris, J. Austin and Messer, O. E. Bronson and Endeve, Eirik and Blondin, John M. and Chertkow, Merek Austin and Lingerfelt, Eric J. and et al.}, year={2016}, month={Feb}, pages={123} }
 @inproceedings{mezzacappa_lentz_bruenn_hix_messer_endeve_blondin_harris_marronetti_yakunin_et al._2015, title={A three-dimensional neutrino-driven core collapse supernova explosion of a 15 M-circle dot star}, volume={498}, booktitle={Numerical modeling of space plasma flows: astronum-2014}, author={Mezzacappa, A. and Lentz, E. J. and Bruenn, S. W. and Hix, W. R. and Messer, O. E. B. and Endeve, E. and Blondin, J. M. and Harris, J. A. and Marronetti, P. and Yakunin, K. N. and et al.}, year={2015}, pages={108–114} }
 @article{yakunin_mezzacappa_marronetti_yoshida_bruenn_hix_lentz_messer_harris_endeve_et al._2015, title={Gravitational wave signatures of ab initio two-dimensional core collapse supernova explosion models for 12-25 M-circle dot stars}, volume={92}, ISSN={["1550-2368"]}, DOI={10.1103/physrevd.92.084040}, abstractNote={Here, we present the gravitational waveforms computed in ab initio two-dimensional core collapse supernova models evolved with the chimera code for progenitor masses between 12 and 25 M. For all models employ multifrequency neutrino transport in the ray-by-ray approximation, state-of-the-art weak interaction physics, relativistic transport corrections such as the gravitational redshift of neutrinos, two-dimensional hydrodynamics with the commensurate relativistic corrections, Newtonian self-gravity with a general-relativistic monopole correction, and the Lattimer-Swesty equation of state with 220 MeV compressibility, and begin with the most recent Woosley-Heger nonrotating progenitors in this mass range. All of our models exhibit robust explosions. Moreover, our waveforms capture all stages of supernova development: 1) a relatively short and weak prompt signal, 2) a quiescent stage, 3) a strong signal due to convection and standing accretion shock instability activity, 4) termination of active accretion onto the proto-neutron star, and 5) a slowly increasing tail that reaches a saturation value. Fourier decomposition shows that the gravitational wave signals we predict should be observable by AdvLIGO for Galactic events across the range of progenitors considered here. The fundamental limitation of these models is in their imposition of axisymmetry. Further progress will require counterpart three-dimensional models, which are underway.}, number={8}, journal={PHYSICAL REVIEW D}, author={Yakunin, Konstantin N. and Mezzacappa, Anthony and Marronetti, Pedro and Yoshida, Shin'ichirou and Bruenn, Stephen W. and Hix, W. Raphael and Lentz, Eric J. and Messer, O. E. Bronson and Harris, J. Austin and Endeve, Eirik and et al.}, year={2015}, month={Oct} }
 @article{temim_slane_kolb_blondin_hughes_bucciantini_2015, title={LATE-TIME EVOLUTION OF COMPOSITE SUPERNOVA REMNANTS: DEEP CHANDRA OBSERVATIONS AND HYDRODYNAMICAL MODELING OF A CRUSHED PULSAR WIND NEBULA IN SNR G327.1-1.1}, volume={808}, DOI={10.1088/0004-637X/808/1/100}, abstractNote={In an effort to better understand the evolution of composite supernova remnants (SNRs) and the eventual fate of relativistic particles injected by their pulsars, we present a multifaceted investigation of the interaction between a pulsar wind nebula (PWN) and its host SNR G327.1-1.1. Our 350 Chandra X-ray observations of SNR G327.1-1.1 reveal a highly complex morphology: a cometary structure resembling a bow shock, prong-like features extending into large arcs in the SNR interior, and thermal emission from the SNR shell. Spectral analysis of the non-thermal emission offers clues about the origin of the PWN structures, while enhanced abundances in the PWN region provide evidence for a mixing of supernova ejecta with PWN material. The overall morphology and spectral properties of the SNR suggest that the PWN has undergone an asymmetric interaction with the SNR reverse shock (RS), whichcan occur as a result of a density gradient in the ambient medium and/or a moving pulsar that displaces the PWN from the center of the remnant. We present hydrodynamical simulations of G327.1-1.1 that show that its morphology and evolution can be described by a ∼17,000-year-old composite SNR that expanded into a density gradient with an orientation perpendicular to the pulsar’s motion. We also show that the RS/PWN interaction scenario can reproduce the broadband spectrum of the PWN from radio to γ-ray wavelengths. The analysis and modeling presented in this work have important implications for our general understanding of the structure and evolution of composite SNRs.}, number={1}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Temim, Tea and Slane, Patrick and Kolb, Christopher and Blondin, John and Hughes, John P. and Bucciantini, Niccoló}, year={2015}, month={Jul}, pages={100} }
 @article{lentz_bruenn_hix_mezzacappa_messer_endeve_blondin_harris_marronetti_yakunin_et al._2015, title={THREE-DIMENSIONAL CORE-COLLAPSE SUPERNOVA SIMULATED USING A 15M⊙PROGENITOR}, volume={807}, ISSN={2041-8213}, url={http://dx.doi.org/10.1088/2041-8205/807/2/L31}, DOI={10.1088/2041-8205/807/2/l31}, abstractNote={ABSTRACT}, number={2}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Lentz, Eric J. and Bruenn, Stephen W. and Hix, W. Raphael and Mezzacappa, Anthony and Messer, O. E. Bronson and Endeve, Eirik and Blondin, John M. and Harris, J. Austin and Marronetti, Pedro and Yakunin, Konstantin N. and et al.}, year={2015}, month={Jul}, pages={L31} }
 @article{kallman_dorodnitsyn_blondin_2015, title={X-RAY POLARIZATION FROM HIGH-MASS X-RAY BINARIES}, volume={815}, ISSN={["1538-4357"]}, DOI={10.1088/0004-637x/815/1/53}, abstractNote={X-ray astronomy allows study of objects that may be associated with compact objects, i.e., neutron stars or black holes, and also may contain strong magnetic fields. Such objects are categorically nonspherical, and likely noncircular when projected on the sky. Polarization allows study of such geometric effects, and X-ray polarimetry is likely to become feasible for a significant number of sources in the future. Potential targets for future X-ray polarization observations are the high-mass X-ray binaries (HMXBs), which consist of a compact object in orbit with an early-type star. In this paper we show that X-ray polarization from HMXBs has a distinct signature that depends on the source inclination and orbital phase. The presence of the X-ray source displaced from the star creates linear polarization even if the primary wind is spherically symmetric whenever the system is viewed away from conjunction. Direct X-rays dilute this polarization whenever the X-ray source is not eclipsed; at mid-eclipse the net polarization is expected to be small or zero if the wind is circularly symmetric around the line of centers. Resonance line scattering increases the scattering fraction, often by large factors, over the energy band spanned by resonance lines. Real winds are not expected to be spherically symmetric, or circularly symmetric around the line of centers, owing to the combined effects of the compact object gravity and ionization on the wind hydrodynamics. A sample calculation shows that this creates polarization fractions ranging up to tens of percent at mid-eclipse.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, publisher={IOP Publishing}, author={Kallman, T. and Dorodnitsyn, A. and Blondin, J.}, year={2015}, month={Dec} }
 @article{manousakis_walter_blondin_2014, title={Accretion in supergiant High Mass X-ray Binaries}, volume={64}, ISSN={2100-014X}, url={http://dx.doi.org/10.1051/EPJCONF/20136402006}, DOI={10.1051/EPJCONF/20136402006}, abstractNote={Supergiant High Mass X-ray Binary systems (sgHMXBs) consist of a massive, late type, star and a neutron star. The massive stars exhibits strong, radiatively driven, stellar winds. Wind accretion onto compact object triggers X-ray emission, which alters the stellar wind significantly. Hydrodynamic simulation has been used to study the neu- tron star - stellar wind interaction it two sgHMXBs: i) A heavily obscured sgHMXB (IGR J17252 3616) discovered by INTEGRAL. To account for observable quantities (i.e., ab- sorbing column density) we have to assume a very slow wind terminal velocity of about 500 km/s and a rather massive neutron star. If confirmed in other obscured systems, this could provide a completely new stellar wind diagnostics. ii) A classical sgHMXB (Vela X-1) has been studied in depth to understand the origin of the o -states observed in this system. Among many models used to account for this observed behavior (clumpy wind, gating mechanism) we propose that self-organized criticality of the accretion stream is the likely reason for the observed behavior. In conclusion, the neutron star, in these two examples, acts very e ciently as a probe to study stellar winds.}, journal={EPJ Web of Conferences}, publisher={EDP Sciences}, author={Manousakis, Antonios and Walter, Roland and Blondin, John}, editor={Bozzo, E. and Kretschmar, P. and Audard, M. and Falanga, M. and Ferrigno, C.Editors}, year={2014}, pages={02006} }
 @article{hix_lentz_endeve_baird_chertkow_harris_messer_mezzacappa_bruenn_blondin_et al._2014, title={Essential ingredients in core-collapse supernovae}, volume={4}, ISSN={["2158-3226"]}, DOI={10.1063/1.4870009}, abstractNote={Carrying 1044 joules of kinetic energy and a rich mix of newly synthesized atomic nuclei, core-collapse supernovae are the preeminent foundries of the nuclear species which make up our solar system and ourselves. Signaling the inevitable death of a massive star, and the birth of a neutron star or black hole, core-collapse supernovae combine physics over a wide range in spatial scales, from kilometer-sized hydrodynamic motions (eventually growing to gigameter scale) down to femtometer-scale nuclear reactions. We will discuss our emerging understanding of the convectively-unstable, neutrino-driven explosion mechanism, based on increasingly realistic neutrino radiation hydrodynamic simulations that include progressively better nuclear and particle physics. Multi-dimensional models with spectral neutrino transport from several research groups, which slowly develop successful explosions for a range of progenitors, have recently motivated changes in our understanding of the neutrino reheating mechanism. In a similar fashion, improvements in nuclear physics, most notably explorations of weak interactions on nuclei and the nuclear equation of state, continue to refine our understanding of the births of neutron stars and the supernovae that result. Recent progress on both the macroscopic and microscopic effects that affect core-collapse supernovae are discussed.}, number={4}, journal={AIP ADVANCES}, author={Hix, W. R. and Lentz, E. J. and Endeve, E. and Baird, M. and Chertkow, M. A. and Harris, J. A. and Messer, O. E. B. and Mezzacappa, A. and Bruenn, S. and Blondin, J. and et al.}, year={2014}, month={Apr} }
 @article{blondin_2013, title={ACCRETION DISKS IN TWO-DIMENSIONAL HOYLE-LYTTLETON FLOW}, volume={767}, ISSN={["0004-637X"]}, DOI={10.1088/0004-637x/767/2/135}, abstractNote={We investigate the flip-flop instability observed in two-dimensional planar hydrodynamic simulations of Hoyle–Lyttleton accretion in the case of an accreting object with a radius much smaller than the nominal accretion radius, as one would expect in astrophysically relevant situations. Contrary to previous results with larger accretors, accretion from a homogenous medium onto a small accretor is characterized by a robust, quasi-Keplerian accretion disk. For gas with a ratio of specific heats of 5/3, such a disk remains locked in one direction for a uniform ambient medium. The accretion flow is more variable for gas with a ratio of specific heats of 4/3, with more dynamical interaction of the disk flow with the bow shock leading to occasional flips in the direction of rotation of the accretion disk. In both cases the accretion of angular momentum is determined by the flow pattern behind the accretion shock rather than by the parameters of the upstream flow.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Blondin, John M.}, year={2013}, month={Apr} }
 @article{bruenn_mezzacappa_hix_lentz_messer_lingerfelt_blondin_endeve_marronetti_yakunin_et al._2013, title={AXISYMMETRIC AB INITIO CORE-COLLAPSE SUPERNOVA SIMULATIONS OF 12-25M☉STARS}, volume={767}, ISSN={2041-8205 2041-8213}, url={http://dx.doi.org/10.1088/2041-8205/767/1/L6}, DOI={10.1088/2041-8205/767/1/l6}, abstractNote={We present an overview of four ab initio axisymmetric core-collapse supernova simulations employing detailed spectral neutrino transport computed with our Chimera code and initiated from Woosley & Heger progenitors of mass 12, 15, 20, and 25 M☉. All four models exhibit shock revival over ∼200 ms (leading to the possibility of explosion), driven by neutrino energy deposition. Hydrodynamic instabilities that impart substantial asymmetries to the shock aid these revivals, with convection appearing first in the 12 M☉ model and the standing accretion shock instability appearing first in the 25 M☉ model. Three of the models have developed pronounced prolate morphologies (the 20 M☉ model has remained approximately spherical). By 500 ms after bounce the mean shock radii in all four models exceed 3000 km and the diagnostic explosion energies are 0.33, 0.66, 0.65, and 0.70 Bethe (B = 1051 erg) for the 12, 15, 20, and 25 M☉ models, respectively, and are increasing. The three least massive of our models are already sufficiently energetic to completely unbind the envelopes of their progenitors (i.e., to explode), as evidenced by our best estimate of their explosion energies, which first become positive at 320, 380, and 440 ms after bounce. By 850 ms the 12 M☉ diagnostic explosion energy has saturated at 0.38 B, and our estimate for the final kinetic energy of the ejecta is ∼0.3 B, which is comparable to observations for lower mass progenitors.}, number={1}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Bruenn, Stephen W. and Mezzacappa, Anthony and Hix, W. Raphael and Lentz, Eric J. and Messer, O. E. Bronson and Lingerfelt, Eric J. and Blondin, John M. and Endeve, Eirik and Marronetti, Pedro and Yakunin, Konstantin N. and et al.}, year={2013}, month={Mar}, pages={L6} }
 @article{williams_borkowski_ghavamian_hewitt_mao_petre_reynolds_blondin_2013, title={AZIMUTHAL DENSITY VARIATIONS AROUND THE RIM OF TYCHO's SUPERNOVA REMNANT}, volume={770}, ISSN={["1538-4357"]}, DOI={10.1088/0004-637x/770/2/129}, abstractNote={Spitzer images of Tycho's supernova remnant in the mid-infrared reveal limb-brightened emission from the entire periphery of the shell and faint filamentary structures in the interior. As with other young remnants, this emission is produced by dust grains, warmed to ∼100 K in the post-shock environment by collisions with energetic electrons and ions. The ratio of the 70 to 24 μm fluxes is a diagnostic of the dust temperature, which in turn is a sensitive function of the plasma density. We find significant variations in the 70/24 flux ratio around the periphery of Tycho's forward shock, implying order-of-magnitude variations in density. While some of these are likely localized interactions with dense clumps of the interstellar medium (ISM), we find an overall gradient in the ambient density surrounding Tycho, with densities 3–10 times higher in the northeast than in the southwest. This large density gradient is qualitatively consistent with the variations in the proper motion of the shock observed in radio and X-ray studies. Overall, the mean ISM density around Tycho is quite low (∼0.1–0.2 cm−3), consistent with the lack of thermal X-ray emission observed at the forward shock. We perform two-dimensional hydrodynamic simulations of a Type Ia supernova expanding into a density gradient in the ISM, and find that the overall round shape of the remnant is still easily achievable, even for explosions into significant gradients. However, this leads to an offset of the center of the explosion from the geometric center of the remnant of up to 20%, although lower values of 10% are preferred. The best match with hydrodynamical simulations is achieved if Tycho is located at a large (3–4 kpc) distance in a medium with a mean preshock density of ∼0.2 cm−3. Such preshock densities are obtained for highly (≳ 50%) porous ISM grains.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Williams, Brian J. and Borkowski, Kazimierz J. and Ghavamian, Parviz and Hewitt, John W. and Mao, S. Alwin and Petre, Robert and Reynolds, Stephen P. and Blondin, John M.}, year={2013}, month={Jun} }
 @article{warren_blondin_2013, title={Three-dimensional numerical investigations of the morphology of Type Ia SNRs}, volume={429}, ISSN={1365-2966 0035-8711}, url={http://dx.doi.org/10.1093/mnras/sts566}, DOI={10.1093/mnras/sts566}, abstractNote={We explore the morphology of Type Ia supernova remnants (SNRs) using threedimensional hydrodynamics modeling and an exponential density profile. Our model distinguishes ejecta from the interstellar medium (ISM), and tracks the ionization age of shocked ejecta, both of which allow for additional analysis of the simulated remnants. We also include the adiabatic index as a free parameter, which aects the compressibility of the fluid and emulates the eciency of cosmic ray acceleration by shock fronts. In addition to generating 3-D images of the simulations, we compute line-of-sight projections through the remnants for comparison against observations of Tycho’s SNR and SN 1006. We find that several features observed in these two remnants, such as the separation between the fluid discontinuities and the presence of ejecta knots ahead of the forward shock, can be generated by smooth ejecta without any initial clumpiness. Our results are consistent with SN 1006 being dynamically younger than Tycho’s SNR, and more eciently accelerating cosmic rays at its forward shock. We conclude that clumpiness is not a necessary condition to reproduce many observed features of Type Ia supernova remnants, particularly the radial profiles and the fleecy emission from ejecta at the central region of both remnants.}, number={4}, journal={Monthly Notices of the Royal Astronomical Society}, publisher={Oxford University Press (OUP)}, author={Warren, Donald C. and Blondin, John M.}, year={2013}, month={Jan}, pages={3099–3113} }
 @article{endeve_cardall_budiardja_mezzacappa_blondin_2013, title={Turbulence and magnetic field amplification from spiral SASI modes in core-collapse supernovae}, volume={T155}, ISSN={["1402-4896"]}, DOI={10.1088/0031-8949/2013/t155/014022}, abstractNote={The stationary accretion shock instability (SASI) plays a central role in modern simulations of the explosion phase of core-collapse supernovae (CCSNe). It may be key to realizing neutrino powered explosions, and possibly links birth properties of pulsars (e.g., kick, spin and magnetic field) to supernova dynamics. Using high-resolution magnetohydrodynamic simulations, we study the development of turbulence, and subsequent amplification of magnetic fields in a simplified model of the post-bounce CCSN environment. Turbulence develops from secondary instabilities induced by the SASI. Our simulations suggest that the development of turbulence plays an important role for the subsequent evolution of the SASI. The turbulence also acts to amplify weak magnetic fields via a small-scale dynamo.}, journal={PHYSICA SCRIPTA}, author={Endeve, E. and Cardall, C. Y. and Budiardja, R. D. and Mezzacappa, A. and Blondin, J. M.}, year={2013}, month={Jul} }
 @article{burkey_reynolds_borkowski_blondin_2013, title={X-RAY EMISSION FROM STRONGLY ASYMMETRIC CIRCUMSTELLAR MATERIAL IN THE REMNANT OF KEPLER'S SUPERNOVA}, volume={764}, ISSN={0004-637X 1538-4357}, url={http://dx.doi.org/10.1088/0004-637X/764/1/63}, DOI={10.1088/0004-637x/764/1/63}, abstractNote={Kepler's supernova remnant resulted from a thermonuclear explosion, but is interacting with circumstellar material (CSM) lost from the progenitor system. We describe a statistical technique for isolating X-ray emission due to CSM from that due to shocked ejecta. Shocked CSM coincides well in position with 24 μm emission seen by Spitzer. We find most CSM to be distributed along the bright north rim, but substantial concentrations are also found projected against the center of the remnant, roughly along a diameter with position angle ∼100°. We interpret this as evidence for a disk distribution of CSM before the supernova, with the line of sight to the observer roughly in the disk plane. We present two-dimensional hydrodynamic simulations of this scenario in qualitative agreement with the observed CSM morphology. Our observations require Kepler to have originated in a close binary system with an asymptotic giant branch star companion.}, number={1}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Burkey, Mary T. and Reynolds, Stephen P. and Borkowski, Kazimierz J. and Blondin, John M.}, year={2013}, month={Jan}, pages={63} }
 @article{chertkow_messer_hix_lee_yakunin_marronetti_bruenn_lentz_blondin_mezzacappa_2012, title={Advancements in modeling self-consistent core collapse supernovae with CHIMERA}, volume={402}, DOI={10.1088/1742-6596/402/1/012025}, abstractNote={We discuss advancements in modeling core-collapse supernovae with our code CHIMERA. We describe the status and details of our tracer particle method and its uses for post-processing nucleosynthesis and as a tool for broad core-collapse supernova (CCSN) model analyses. We also introduce our progress towards expanding a nuclear reaction network beyond the alphanetwork for the purpose of accurate in-situ nucleosynthesis, not only for core-collapse supernovae (CCSNe) in general, but for a special sub-class of supernovae called electron capture supernovae (ECSNe), which stem from progenitors stars between 8 and 10 M⊙. By using an advanced nuclear reaction network, our 2D and 3D code will allow for unparalleled studies of CCSNe and ECSNe ejecta.}, journal={Journal of Physics: Conference Series}, publisher={IOP Publishing}, author={Chertkow, M A and Messer, O E B and Hix, W R and Lee, C T and Yakunin, K and Marronetti, P and Bruenn, S W and Lentz, E J and Blondin, J and Mezzacappa, A}, year={2012}, pages={012025} }
 @article{blondin_raymer_2012, title={HOYLE-LYTTLETON ACCRETION IN THREE DIMENSIONS}, volume={752}, ISSN={0004-637X 1538-4357}, url={http://dx.doi.org/10.1088/0004-637X/752/1/30}, DOI={10.1088/0004-637x/752/1/30}, abstractNote={We investigate the stability of gravitational accretion of an ideal gas onto a compact object moving through a uniform medium at Mach 3. Previous three-dimensional simulations have shown that such accretion is not stable, and that strong rotational “disk-like” flows are generated and accreted on short timescales. We re-address this problem using overset spherical grids that provide a factor of seven improvement in spatial resolution over previous simulations. With our higher spatial resolution we found these three-dimensional accretion flows remained remarkably axisymmetric. We examined two cases of accretion with different sized accretors. The larger accretor produced very steady flow, with the mass accretion rate varying by less than 0.02% over 30 flow times. The smaller accretor exhibited an axisymmetric breathing mode that modulated the mass accretion rate by a constant 20%. Nonetheless, the flow remained highly axisymmetric with only negligible accretion of angular momentum in both cases.}, number={1}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Raymer, Eric}, year={2012}, month={May}, pages={30} }
 @article{manousakis_walter_blondin_2012, title={Neutron star masses from hydrodynamical effects in obscured supergiant high mass X-ray binaries}, volume={547}, ISSN={0004-6361 1432-0746}, url={http://dx.doi.org/10.1051/0004-6361/201219717}, DOI={10.1051/0004-6361/201219717}, abstractNote={A population of obscured supergiant High Mass X-ray Binaries (sgHMXBs) has been discovered by INTEGRAL. X-ray wind tomography of IGR J17252-3616 inferred a slow wind velocity to account for the enhanced obscuration. The main goal of this study is to understand under which conditions high obscuration could occur. We have used an hydrodynamical code to simulate the flow of the stellar wind around the neutron star. A grid of simulations was used to study the dependency of the absorbing column density and of the X-ray light-curves on the model parameters. A comparison between the simulation results and the observations of IGR J17252-3616 provides an estimate on these parameters. We have constrained the wind terminal velocity to 500-600 km/s and the neutron star mass to 1.75-2.15 solar masses. We have confirmed that the initial hypothesis of a slow wind velocity with a moderate mass loss rate is valid. The mass of the neutron star can be constrained by studying its impact on the accretion flow.}, journal={Astronomy & Astrophysics}, publisher={EDP Sciences}, author={Manousakis, A. and Walter, R. and Blondin, J. M.}, year={2012}, month={Oct}, pages={A20} }
 @article{endeve_cardall_budiardja_beck_bejnood_toedte_mezzacappa_blondin_2012, title={TURBULENT MAGNETIC FIELD AMPLIFICATION FROM SPIRAL SASI MODES: IMPLICATIONS FOR CORE-COLLAPSE SUPERNOVAE AND PROTO-NEUTRON STAR MAGNETIZATION}, volume={751}, ISSN={["1538-4357"]}, DOI={10.1088/0004-637x/751/1/26}, abstractNote={We extend our investigation of magnetic field evolution in three-dimensional flows driven by the stationary accretion shock instability (SASI) with a suite of higher-resolution idealized models of the post-bounce core-collapse supernova environment. Our magnetohydrodynamic simulations vary in initial magnetic field strength, rotation rate, and grid resolution. Vigorous SASI-driven turbulence inside the shock amplifies magnetic fields exponentially; but while the amplified fields reduce the kinetic energy of small-scale flows, they do not seem to affect the global shock dynamics. The growth rate and final magnitude of the magnetic energy are very sensitive to grid resolution, and both are underestimated by the simulations. Nevertheless, our simulations suggest that neutron star magnetic fields exceeding 1014 G can result from dynamics driven by the SASI, even for non-rotating progenitors.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Endeve, Eirik and Cardall, Christian Y. and Budiardja, Reuben D. and Beck, Samuel W. and Bejnood, Alborz and Toedte, Ross J. and Mezzacappa, Anthony and Blondin, John M.}, year={2012}, month={May} }
 @article{williams_blair_blondin_borkowski_ghavamian_long_raymond_reynolds_rho_winkler_et al._2011, title={RCW 86: A TYPE Ia SUPERNOVA IN A WIND-BLOWN BUBBLE}, volume={741}, ISSN={["1538-4357"]}, DOI={10.1088/0004-637x/741/2/96}, abstractNote={We report results from a multi-wavelength analysis of the Galactic supernova remnant RCW 86, the proposed remnant of the supernova of 185 A.D. We show new infrared observations from the Spitzer Space Telescope and the Wide-Field Infrared Survey Explorer, where the entire shell is detected at 24 and 22 μm. We fit the infrared flux ratios with models of collisionally heated ambient dust, finding post-shock gas densities in the non-radiative shocks of 2.4 and 2.0 cm−3 in the southwest (SW) and northwest (NW) portions of the remnant, respectively. The Balmer-dominated shocks around the periphery of the shell, large amount of iron in the X-ray-emitting ejecta, and lack of a compact remnant support a Type Ia origin for this remnant. From hydrodynamic simulations, the observed characteristics of RCW 86 are successfully reproduced by an off-center explosion in a low-density cavity carved by the progenitor system. This would make RCW 86 the first known case of a Type Ia supernova in a wind-blown bubble. The fast shocks (>3000 km s−1) observed in the northeast are propagating in the low-density bubble, where the shock is just beginning to encounter the shell, while the slower shocks elsewhere have already encountered the bubble wall. The diffuse nature of the synchrotron emission in the SW and NW is due to electrons that were accelerated early in the lifetime of the remnant, when the shock was still in the bubble. Electrons in a bubble could produce gamma rays by inverse-Compton scattering. The wind-blown bubble scenario requires a single-degenerate progenitor, which should leave behind a companion star.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Williams, B. J. and Blair, W. P. and Blondin, J. M. and Borkowski, K. J. and Ghavamian, P. and Long, K. S. and Raymond, J. C. and Reynolds, S. P. and Rho, J. and Winkler, P. F. and et al.}, year={2011}, month={Nov} }
 @article{yakunin_marronetti_mezzacappa_bruenn_lee_chertkow_hix_blondin_lentz_messer_et al._2010, title={Gravitational waves from core collapse supernovae}, volume={27}, ISSN={["1361-6382"]}, DOI={10.1088/0264-9381/27/19/194005}, abstractNote={We present the gravitational wave signatures for a suite of axisymmetric core collapse supernova models with progenitor masses between 12 and 25 M⊙. These models are distinguished by the fact that they explode and contain essential physics (in particular, multi-frequency neutrino transport and general relativity) needed for a more realistic description. Thus, we are able to compute complete waveforms (i.e. through explosion) based on non-parameterized, first-principles models. This is essential if the waveform amplitudes and time scales are to be computed more precisely. Fourier decomposition shows that the gravitational wave signals we predict should be observable by AdvLIGO across the range of progenitors considered here. The fundamental limitation of these models is in their imposition of axisymmetry. Further progress will require counterpart three-dimensional models.}, number={19}, journal={CLASSICAL AND QUANTUM GRAVITY}, author={Yakunin, Konstantin N. and Marronetti, Pedro and Mezzacappa, Anthony and Bruenn, Stephen W. and Lee, Ching-Tsai and Chertkow, Merek A. and Hix, W. Raphael and Blondin, John M. and Lentz, Eric J. and Messer, O. E. Bronson and et al.}, year={2010}, month={Oct} }
 @article{hix_lentz_baird_messer_mezzacappa_lee_bruenn_blondin_marronetti_2010, title={Understanding Core-Collapse Supernovae}, volume={834}, ISSN={["1873-1554"]}, DOI={10.1016/j.nuclphysa.2010.01.104}, abstractNote={Our understanding of core-collapse supernovae continues to improve as better microphysics is included in increasingly realistic neutrino-radiationhydrodynamic simulations. Recent multi-dimensional models with spectral neutrino transport, which slowly develop successful explosions for a range of progenitors between 12 and 25 solar mass, have motivated changes in our understanding of the neutrino reheating mechanism. In a similar fashion, improvements in nuclear physics, most notably explorations of weak interactions on nuclei and the nuclear equation of state, continue to refine our understanding of how supernovae explode. Recent progresses on both the macroscopic and microscopic effects that affect core-collapse supernovae are discussed.}, number={1-4}, journal={NUCLEAR PHYSICS A}, author={Hix, W. R. and Lentz, E. J. and Baird, M. and Messer, O. E. B. and Mezzacappa, A. and Lee, C-T and Bruenn, S. W. and Blondin, J. M. and Marronetti, P.}, year={2010}, month={Mar}, pages={602C–607C} }
 @article{bruenn_mezzacappa_hix_blondin_marronetti_messer_dirk_yoshida_2009, title={2D and 3D core-collapse supernovae simulation results obtained with the CHIMERA code}, volume={180}, DOI={10.1088/1742-6596/180/1/012018}, abstractNote={Much progress in realistic modeling of core-collapse supernovae has occurred recently through the availability of multi-teraflop machines and the increasing sophistication of supernova codes. These improvements are enabling simulations with enough realism that the explosion mechanism, long a mystery, may soon be delineated. We briefly describe the CHIMERA code, a supernova code we have developed to simulate core-collapse supernovae in 1, 2, and 3 spatial dimensions. We then describe the results of an ongoing suite of 2D simulations initiated from a 12, 15, 20, and 25 M⊙ progenitor. These have all exhibited explosions and are currently in the expanding phase with the shock at between 5,000 and 20,000 km. We also briefly describe an ongoing simulation in 3 spatial dimensions initiated from the 15 M⊙ progenitor.}, journal={Journal of Physics: Conference Series}, publisher={IOP Publishing}, author={Bruenn, S W and Mezzacappa, A and Hix, W R and Blondin, J M and Marronetti, P and Messer, O E B and Dirk, C J and Yoshida, S}, year={2009}, month={Aug}, pages={012018} }
 @article{borkowski_blondin_reynolds_2009, title={CIRCUMSTELLAR SHELLS IN ABSORPTION IN TYPE Ia SUPERNOVAE}, volume={699}, ISSN={["2041-8213"]}, DOI={10.1088/0004-637X/699/2/L64}, abstractNote={Progenitors of Type Ia supernovae (SNe) have been predicted to modify their ambient circumstellar (CSM) and interstellar environments through the action of their powerful winds. While there is X-ray and optical evidence for circumstellar interaction in several remnants of Type Ia SNe, widespread evidence for such interaction in Type Ia SNe themselves has been lacking. We consider prospects for the detection of CSM shells that have been predicted to be common around Type Ia SNe. Such shells are most easily detected in Na I absorption lines. Variable (declining) absorption is expected to occur soon after the explosion, primarily during the SN rise time, for shells located within ∼1–10 pc of a SN. The distance of the shell from the SN can be determined by measuring the timescale for line variability.}, number={2}, journal={ASTROPHYSICAL JOURNAL LETTERS}, publisher={IOP Publishing}, author={Borkowski, Kazimierz J. and Blondin, John M. and Reynolds, Stephen P.}, year={2009}, month={Jul}, pages={L64–L67} }
 @article{blondin_pope_2009, title={REVISITING THE "FLIP-FLOP" INSTABILITY OF HOYLE-LYTTLETON ACCRETION}, volume={700}, ISSN={["0004-637X"]}, DOI={10.1088/0004-637X/700/1/95}, abstractNote={We revisit the flip-flop instability of two-dimensional planar accretion using high-fidelity numerical simulations. By starting from an initially steady-state axisymmetric solution, we are able to follow the growth of this overstability from small amplitudes. In the small-amplitude limit, before any transient accretion disk is formed, the oscillation period of the accretion shock is comparable to the Keplerian period at the Hoyle–Lyttleton accretion radius (Ra), independent of the size of the accreting object. The growth rate of the overstability increases dramatically with decreasing size of the accretor, but is relatively insensitive to the upstream Mach number of the flow. We confirm that the flip-flop does not require any gradient in the upstream flow. Indeed, a small density gradient as used in the discovery simulations has virtually no influence on the growth rate of the overstability. The ratio of specific heats does influence the overstability, with smaller γ leading to faster growth of the instability. For a relatively large accretor (a radius of 0.037 Ra) planar accretion is unstable for γ = 4/3, but stable for γ ⩾ 1.6. Planar accretion is unstable even for γ = 5/3 provided the accretor has a radius of < 0.0025 Ra. We also confirm that when the accretor is sufficiently small, the secular evolution is described by sudden jumps between states with counter-rotating quasi-Keplerian accretion disks.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, publisher={IOP Publishing}, author={Blondin, John M. and Pope, T. Chris}, year={2009}, month={Jul}, pages={95–102} }
 @article{messer_bruenn_blondin_hix_mezzacappa_2008, title={Multidimensional, multiphysics simulations of core—collapse supernovae}, volume={125}, DOI={10.1088/1742-6596/125/1/012010}, abstractNote={CHIMERA is a multi-dimensional radiation hydrodynamics code designed to study core-collapse supernovae. The code is made up of three essentially independent parts: a hydrodynamics module, a nuclear burning module, and a neutrino transport solver combined within an operator-split approach. We review the code's architecture and some recently improved implementations used in the code. We also briefly discuss preliminary results obtained with the code in three spatial dimensions.}, journal={Journal of Physics: Conference Series}, publisher={IOP Publishing}, author={Messer, O E B and Bruenn, S W and Blondin, J M and Hix, W R and Mezzacappa, A}, year={2008}, month={Aug}, pages={012010} }
 @article{reynolds_borkowski_hwang_hughes_badenes_laming_blondin_2007, title={A deep Chandra observation of Kepler's supernova remnant: A type IA event with circumstellar interaction}, volume={668}, ISSN={["1538-4357"]}, DOI={10.1086/522830}, abstractNote={We present initial results of a 750 ks Chandra observation of the remnant of Kepler's supernova of AD 1604. The strength and prominence of iron emission, together with the absence of O-rich ejecta, demonstrate that Kepler resulted from a thermonuclear supernova, even though evidence for circumstellar interaction is also strong. We have analyzed spectra of over 100 small regions, and find that they fall into three classes. (1) The vast majority show Fe L emission between 0.7 and 1 keV and Si and S Kα emission; we associate these with shocked ejecta. A few of these are found at or beyond the mean blast wave radius. (2) A very few regions show solar O/Fe abundance ratios; these we associate with shocked circumstellar medium (CSM). Otherwise O is scarce. (3) A few regions are dominated by continuum, probably synchrotron radiation. Finally, we find no central point source, with a limit ~100 times fainter than the central object in Cas A. The evidence that the blast wave is interacting with CSM may indicate a Ia explosion in a more massive progenitor.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Reynolds, Stephen P. and Borkowski, Kazimierz J. and Hwang, Una and Hughes, John P. and Badenes, Carles and Laming, J. M. and Blondin, J. M.}, year={2007}, month={Oct}, pages={L135–L138} }
 @inproceedings{mezzacappa_bruenn_blondin_hix_bronson messer_2007, title={Ascertaining the Core Collapse Supernova Mechanism: An Emerging Picture?}, url={http://dx.doi.org/10.1063/1.2774864}, DOI={10.1063/1.2774864}, abstractNote={The mechanism for core collapse supernova explosions remains undefined in detail and perhaps even in broad brush. Past multidimensional simulations point to the important role neutrino transport, fluid instabilities, rotation, and magnetic fields play, or may play, in generating core collapse supernova explosions, but the fundamental question as to whether or not these events are powered by neutrinos with the aid of some or all of these other phenomena or by magnetic fields or by a combination of both is unanswered. Here we present the results from two sets of simulations, in two and three spatial dimensions. In two dimensions, the simulations include multifrequency flux‐limited diffusion neutrino transport in the “ray‐by‐ray‐plus” approximation, two‐dimensional self gravity in the Newtonian limit, and nuclear burning through a 14‐isotope alpha network. The three‐dimensional simulations are model simulations constructed to reflect the post stellar core bounce conditions during neutrino shock reheating at ...}, publisher={American Institute of Physics}, author={Mezzacappa, Anthony and Bruenn, Stephen W. and Blondin, John M. and Hix, W. Raphael and Bronson Messer, O. E.}, year={2007} }
 @article{blondin_shaw_2007, title={Linear growth of spiral SASI modes in core-collapse supernovae}, volume={656}, ISSN={["1538-4357"]}, DOI={10.1086/510614}, abstractNote={Two-dimensional axisymmetric simulations have shown that the postbounce accretion shock in core-collapse supernovae is subject to the spherical accretion shock instability, or SASI. Recent three-dimensional simulations have revealed the existence of a nonaxisymmetric mode of the SASI as well, where the postshock flow displays a spiral pattern. Here we investigate the growth of these spiral modes using two-dimensional simulations of the postbounce accretion flow in the equatorial plane of a core-collapse supernova. By perturbing a steady state model we are able to excite both one-, two-, and three-armed spiral modes that grow exponentially with time, demonstrating that these are linearly unstable modes closely related to the original axisymmetric sloshing modes. By tracking the distribution of angular momentum, we show that these modes are able to efficiently separate the angular momentum of the accretion flow (which maintains a net angular momentum of zero), leading to a significant spin-up of the underlying accreting proto-neutron star.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Blondin, John M. and Shaw, Samantha}, year={2007}, month={Feb}, pages={366–371} }
 @article{messer_bruenn_blondin_hix_mezzacappa_dirk_2007, title={Petascale supernova simulation with CHIMERA}, volume={78}, DOI={10.1088/1742-6596/78/1/012049}, abstractNote={CHIMERA is a multi-dimensional radiation hydrodynamics code designed to study core-collapse supernovae. The code is made up of three essentially independent parts: a hydrodynamics module, a nuclear burning module, and a neutrino transport solver combined within an operator-split approach. We describe some major algorithmic facets of the code and briefly discuss some recent results. The multi-physics nature of the problem, and the specific implementation of that physics in CHIMERA, provide a rather straightforward path to effective use of multi-core platforms in the near future.}, journal={Journal of Physics: Conference Series}, publisher={IOP Publishing}, author={Messer, O E B and Bruenn, S W and Blondin, J M and Hix, W R and Mezzacappa, A and Dirk, C J}, year={2007}, month={Aug}, pages={012049} }
 @article{blondin_mezzacappa_2007, title={Pulsar spins from an instability in the accretion shock of supernovae}, volume={445}, ISSN={["1476-4687"]}, DOI={10.1038/nature05428}, abstractNote={Rotation-powered radio pulsars are born with inferred initial rotation periods of order 300 ms (some as short as 20 ms) in core-collapse supernovae. In the traditional picture, this fast rotation is the result of conservation of angular momentum during the collapse of a rotating stellar core. This leads to the inevitable conclusion that pulsar spin is directly correlated with the rotation of the progenitor star. So far, however, stellar theory has not been able to explain the distribution of pulsar spins, suggesting that the birth rotation is either too slow or too fast. Here we report a robust instability of the stalled accretion shock in core-collapse supernovae that is able to generate a strong rotational flow in the vicinity of the accreting proto-neutron star. Sufficient angular momentum is deposited on the proto-neutron star to generate a final spin period consistent with observations, even beginning with spherically symmetrical initial conditions. This provides a new mechanism for the generation of neutron star spin and weakens, if not breaks, the assumed correlation between the rotational periods of supernova progenitor cores and pulsar spin.}, number={7123}, journal={NATURE}, author={Blondin, John M. and Mezzacappa, Anthony}, year={2007}, month={Jan}, pages={58–60} }
 @article{akashi_soker_behar_blondin_2007, title={X-ray emission from planetary nebulae calculated by 1D spherical numerical simulations}, volume={375}, ISSN={["1365-2966"]}, DOI={10.1111/j.1365-2966.2006.11267.x}, abstractNote={We calculate the X-ray emission from both constant and time-evolving shocked fast winds blown by the central stars of planetary nebulae (PNe) and compare our calculations with observations. Using spherically symmetric numerical simulations with radiative cooling, we calculate the flow structure and the X-ray temperature and luminosity of the hot bubble formed by the shocked fast wind. We find that a constant fast wind gives results that are very close to those obtained from the self-similar solution. We show that in order for a fast shocked wind to explain the observed X-ray properties of PNe, rapid evolution of the wind is essential. More specifically, the mass-loss rate of the fast wind should be high early on when the speed is ∼300-700 km s -1 , and then it needs to drop drastically by the time the PN age reaches ∼ 1000 yr. This implies that the central star has a very short pre-PN (post-asymptotic giant branch) phase.}, number={1}, journal={MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY}, author={Akashi, M. and Soker, Noam and Behar, Ehud and Blondin, John}, year={2007}, month={Feb}, pages={137–144} }
 @article{bruenn_dirk_mezzacappa_hayes_blondin_hix_messer_2006, title={Modeling core collapse supernovae in 2 and 3 dimensions with spectral neutrino transport}, volume={46}, DOI={10.1088/1742-6596/46/1/054}, abstractNote={The overwhelming evidence that the core collapse supernova mechanism is inherently multidimensional, the complexity of the physical processes involved, and the increasing evidence from simulations that the explosion is marginal presents great computational challenges for the realistic modeling of this event, particularly in 3 spatial dimensions. We have developed a code scalable to computations in 3 dimensions that couples PPM Lagrangian-withremap hydrodynamics, multigroup flux-limited diffusion neutrino transport (with many improvements), and a nuclear network. The neutrino transport is performed in a ‘‘ray-by-ray-plus’’ approximation, wherein all the lateral effects of neutrinos are included (e.g., pressure, velocity corrections, advection) except lateral transport. A moving radial grid option permits the evolution to be carried out from initial core collapse with only modest demands on the number of radial zones. The inner part of the core is evolved after collapse, along with the rest of the core and mantle, by subcycling the lateral evolution near the center as demanded by the small Courant times. We present results of 2-D simulations of a symmetric and an asymmetric collapse of both a 15 and an 11 M⊙ progenitor. In each of these simulations we have discovered that once the oxygen-rich material reaches the shock there is a synergistic interplay between the reduced ram pressure, the energy released by the burning of the shock-heated oxygen-rich material, and the neutrino energy deposition that leads to a revival of the shock and an explosion.}, journal={Journal of Physics: Conference Series}, publisher={IOP Publishing}, author={Bruenn, S W and Dirk, C J and Mezzacappa, A and Hayes, J C and Blondin, J M and Hix, W R and Messer, O E B}, year={2006}, month={Sep}, pages={393–402} }
 @article{blondin_mezzacappa_2006, title={The spherical accretion shock instability in the linear regime}, volume={642}, ISSN={["1538-4357"]}, DOI={10.1086/500817}, abstractNote={We use time-dependent, axisymmetric, hydrodynamic simulations to study the linear stability of the stalled, spherical accretion shock that arises in the postbounce phase of core-collapse supernovae. We show that this accretion shock is stable to radial modes, with decay rates and oscillation frequencies in close agreement with the linear stability analysis of Houck and Chevalier. For nonspherical perturbations we find that the l = 1 mode is always unstable for parameters appropriate to core-collapse supernovae. We also find that the l = 2 mode is unstable, but typically has a growth rate smaller than that for l = 1. Furthermore, the l = 1 mode is the only mode found to transition into a nonlinear stage in our simulations. This result provides a possible explanation for the dominance of an l = 1 "sloshing" mode seen in many two-dimensional simulations of core-collapse supernovae.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Blondin, JM and Mezzacappa, A}, year={2006}, month={May}, pages={401–409} }
 @article{blondin_2005, title={Discovering new dynamics of core-collapse supernova shock waves}, volume={16}, DOI={10.1088/1742-6596/16/1/051}, abstractNote={There is a growing body of evidence that core collapse supernova explosions are inherently asymmetric. The origin of this asymmetry may arise in the first few hundred milliseconds after core collapse when the nascent shock wave is susceptible to the spherical accretion shock instability, a dynamical instability discovered through computer simulations by the SciDAC-funded Terascale Supernova Initiative. This work was followed up by large-scale 3D simulations enabled by the application of various high-performance computing technologies including networking and visualization. Recent 3D simulations have identified a vigorous non-axisymmetric mode of this supernova shock wave that can impart a significant amount of angular momentum to the underlying neutron star.}, journal={Journal of Physics: Conference Series}, publisher={IOP Publishing}, author={Blondin, John M}, year={2005}, month={Aug}, pages={370–379} }
 @article{rao_carter_qishiwu_wing_zhu_mezzacappa_veeraraghavan_blondin_2005, title={Networking for large-scale science: infrastructure, provisioning, transport and application mapping}, volume={16}, DOI={10.1088/1742-6596/16/1/074}, abstractNote={Large-scale science computations and experiments require unprecedented network capabilities in the form of large bandwidth and dynamically stable connections to support data transfers, interactive visualizations, and monitoring and steering operations. A number of component technologies dealing with the infrastructure, provisioning, transport and application mappings must be developed and/or optimized to achieve these capabilities. We present a brief account of the following technologies that contribute toward achieving these network capabilities: (a) DOE UltraScienceNet and NSF CHEETAH network testbeds that provide on-demand and scheduled dedicated network connections; (b) experimental results on transport protocols that achieve close to 100% utilization on dedicated 1Gbps wide-area channels; (c) a scheme for optimally mapping a visualization pipeline onto a network to minimize the end-to-end delays; and (d) interconnect configuration and protocols that provides multiple Gbps flows from Cray X1 to external hosts.}, journal={Journal of Physics: Conference Series}, publisher={IOP Publishing}, author={Rao, Nageswara S and Carter, Steven M and QishiWu and Wing, William R and Zhu, Mengxia and Mezzacappa, Anthony and Veeraraghavan, Malathi and Blondin, John M}, year={2005}, month={Aug}, pages={541–545} }
 @article{hwang_laming_badenes_berendse_blondin_cioffi_delaney_dewey_fesen_flanagan_et al._2004, title={A million second Chandra view of Cassiopeia A}, volume={615}, ISSN={["1538-4357"]}, DOI={10.1086/426186}, abstractNote={We introduce a million second observation of the supernova remnant Cassiopeia A with the Chandra X-Ray Observatory. The bipolar structure of the Si-rich ejecta (northeast jet and southwest counterpart) is clearly evident in the new images, and their chemical similarity is confirmed by their spectra. These are most likely due to jets of ejecta as opposed to cavities in the circumstellar medium, since we can reject simple models for the latter. The properties of these jets and the Fe-rich ejecta will provide clues to the explosion of Cas A.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Hwang, U and Laming, JM and Badenes, C and Berendse, F and Blondin, J and Cioffi, D and DeLaney, T and Dewey, D and Fesen, R and Flanagan, KA and et al.}, year={2004}, month={Nov}, pages={L117–L120} }
 @article{bucciantini_amato_bandiera_blondin_del zanna_2004, title={Magnetic Rayleigh-Taylor instability for Pulsar Wind Nebulae in expanding Supernova Remnants}, volume={423}, ISSN={["1432-0746"]}, DOI={10.1051/0004-6361:20040360}, abstractNote={We present a numerical investigation of the development of Rayleigh-Taylor instability at the interface between an expanding Pulsar Wind Nebula and its surrounding Supernova Remnant. These systems have long been thought to be naturally subject to this kind of instability, given their expansion behavior and the density jump at the contact discontinuity. High resolution images of the Crab Nebula at optical frequencies show the presence of a complex network of line-emitting filaments protruding inside the synchrotron nebula. These structures are interpreted as the observational evidence that Rayleigh-Taylor instability is in fact at work. The development of this instability in the regime appropriate to describe Supernova Remnant-Pulsar Wind Nebula systems is non-trivial. The conditions at the interface are likely close to the stability threshold, and the inclusion of the nebular magnetic field, which might play an important role in stabilizing the system, is essential to the modeling. If Rayleigh-Taylor features can grow efficiently a mixing layer in the outer portion of the nebula might form where most of the supernova material is confined. When a magnetic field close to equipartition is included we find that the interface is stable, and that even a weaker magnetic field affects substantially the growth and shape of the fingers.}, number={1}, journal={ASTRONOMY & ASTROPHYSICS}, author={Bucciantini, N and Amato, E and Bandiera, R and Blondin, JM and Del Zanna, L}, year={2004}, month={Aug}, pages={253–265} }
 @article{bucciantini_bandiera_blondin_amato_del zanna_2004, title={The effects of spin-down on the structure and evolution of pulsar wind nebulae}, volume={422}, ISSN={["1432-0746"]}, DOI={10.1051/0004-6361:20034400}, abstractNote={We present high resolution spherically symmetric relativistic magnetohydrodynamical simulations of the evolution of a pulsar wind nebula inside the freely expanding ejecta of the supernova progenitor. The evolution is followed starting from a few years after the supernova explosion and up to an age of the remnant of 1500 years. We consider different values of the pulsar wind magnetization parameter and also different braking indices for the spin-down process. We compare the numerical results with those derived through an approximate semi-analytical approach that allows us to trace the time evolution of the positions of both the pulsar wind termination shock and the contact discontinuity between the nebula and the supernova ejecta. We also discuss, whenever a comparison is possible, to what extent our numerical results agree with former self-similar models, and how these models could be adapted to take into account the temporal evolution of the system. The inferred magnetization of the pulsar wind could be an order of magnitude lower than that derived from time independent analytic models.}, number={2}, journal={ASTRONOMY & ASTROPHYSICS}, author={Bucciantini, N and Bandiera, R and Blondin, JM and Amato, E and Del Zanna, L}, year={2004}, month={Aug}, pages={609–619} }
 @article{bucciantini_blondin_del zanna_amato_2003, title={Spherically symmetric relativistic MHD simulations of pulsar wind nebulae in supernova remnants}, volume={405}, ISSN={["1432-0746"]}, DOI={10.1051/0004-6361:20030624}, abstractNote={Pulsars, formed during supernova explosions, are known to be sources of relativistic magnetized winds whose in- teraction with the expanding supernova remnants (SNRs) gives rise to a pulsar wind nebula (PWN). We present spherically symmetric relativistic magnetohydrodynamics (RMHD) simulations of the interaction of a pulsar wind with the surround- ing SNR, both in particle and magnetically dominated regimes. As shown by previous simulations, the evolution can be divided into three phases: free expansion, a transient phase characterized by the compression and reverberation of the reverse shock, and a final Sedov expansion. The evolution of the contact discontinuity between the PWN and the SNR (and consequently of the SNR itself) is almost independent of the magnetization of the nebula as long as the total (magnetic plus particle) energy is the same. However, a dierent behaviour of the PWN internal structure is observable during the compression-reverberation phase, depending on the degree of magnetization. The simulations were performed using the third order conservative scheme by Del Zanna et al. (2003).}, number={2}, journal={ASTRONOMY & ASTROPHYSICS}, author={Bucciantini, N and Blondin, JM and Del Zanna, L and Amato, E}, year={2003}, month={Jul}, pages={617–626} }
 @article{blondin_mezzacappa_demarino_2003, title={Stability of standing accretion shocks, with an eye toward core-collapse supernovae}, volume={584}, ISSN={["0004-637X"]}, DOI={10.1086/345812}, abstractNote={We examine the stability of standing, spherical accretion shocks. Accretion shocks arise in core-collapse supernovae (the focus of this paper), star formation, and accreting white dwarfs and neutron stars. We present a simple analytic model and use time-dependent hydrodynamics simulations to show that this solution is stable to radial perturbations. In two dimensions we show that small perturbations to a spherical shock front can lead to rapid growth of turbulence behind the shock, driven by the injection of vorticity from the now nonspherical shock. We discuss the ramifications this instability may have for the supernova mechanism.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Blondin, JM and Mezzacappa, A and DeMarino, C}, year={2003}, month={Feb}, pages={971–980} }
 @article{blondin_borkowski_reynolds_2001, title={Dynamics of Fe bubbles in young supernova remnants}, volume={557}, ISSN={["0004-637X"]}, DOI={10.1086/321674}, abstractNote={Observations of core-collapse supernovae (SNe) have revealed the presence of extensive mixing of radioactive material in SN ejecta. The mixing of radioactive material, mostly freshly synthesized Ni, is not complete, which leads to a two-phase SN ejecta structure. The low-density phase consists of Fe bubbles, created by the energy input from radioactive Co and Ni, surrounded by compressed high-density metal-rich ejecta. We report on the theoretical investigation of supernova remnant (SNR) dynamics with the two-phase SN ejecta. We first present three-dimensional hydrodynamic simulations of a single Fe bubble immersed in an outer ejecta envelope. We then consider randomly distributed Fe bubbles with an average volume filling fraction of 1/2. We find that the presence of Fe bubbles leads to vigorous turbulence and mixing of Fe with other heavy elements and with the ambient normal-abundance gas. The turbulent energy can be an order of magnitude larger than in the case of smooth ejecta. A significant fraction of the shocked ejecta is found in narrow filaments and clumps moving with radial velocities larger than the velocity of the forward shock. Observational consequences of the two-phase ejecta on SNR X-ray spectra and images are briefly mentioned.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Blondin, JM and Borkowski, KJ and Reynolds, SP}, year={2001}, month={Aug}, pages={782–791} }
 @article{blondin_chevalier_frierson_2001, title={Pulsar wind nebulae in evolved supernova remnants}, volume={563}, ISSN={["0004-637X"]}, DOI={10.1086/324042}, abstractNote={For pulsars similar to the one in the Crab Nebula, most of the energy input to the surrounding wind nebula occurs on a timescale ≲103 yr; during this time, the nebula expands into freely expanding supernova ejecta. On a timescale ~104 yr, the interaction of the supernova with the surrounding medium drives a reverse shock front toward the center of the remnant, where it crushes the pulsar wind nebula (PWN). We have carried out one- and two-dimensional, two-fluid simulations of the crushing and reexpansion phases of a PWN. We show that (1) these phases are subject to Rayleigh-Taylor instabilities that result in the mixing of thermal and nonthermal fluids, and (2) asymmetries in the surrounding interstellar medium give rise to asymmetries in the position of the PWN relative to the pulsar and explosion site. These effects are expected to be observable in the radio emission from evolved PWN because of the long lifetimes of radio-emitting electrons. The scenario can explain the chaotic and asymmetric appearance of the Vela X PWN relative to the Vela pulsar without recourse to a directed flow from the vicinity of the pulsar. The displacement of the radio nebulae in G327.1-1.1, MSH 15-56 (G326.3-1.8), G0.9+0.1, and W44 relative to the X-ray nebulae may be due to this mechanism. On timescales much greater than the nebular crushing time, the initial PWN may be mixed with thermal gas and become unobservable, so that even the radio emission is dominated by recently injected particles.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Blondin, JM and Chevalier, RA and Frierson, DM}, year={2001}, month={Dec}, pages={806–815} }
 @article{blondin_ellison_2001, title={Rayleigh-Taylor instabilities in young supernova remnants undergoing efficient particle acceleration}, volume={560}, ISSN={["0004-637X"]}, DOI={10.1086/322499}, abstractNote={We employ hydrodynamic simulations to study the effects of high shock compression ratios, as expected for fast shocks with efficient particle acceleration, on the convective instability of driven waves in supernova remnants. We find that the instability itself does not depend significantly on the compression ratio, σ, with the growth rates and the width of the mixing region at saturation being comparable for the range of ratios we studied; 4 ≤ σ ≤ 21. However, because the width of the interaction region between the forward and reverse shocks can shrink significantly with increasing σ, we find that convective instabilities can reach all the way to the forward shock front if compression ratios are high enough. Thus, if supernova blast waves accelerate particles efficiently, we expect the forward shock to be perturbed with small-amplitude, small-wavelength bumps and to find clumps and filaments of dense ejecta material in the vicinity of the shock. In addition and in contrast to situations in which σ ≤ 4, any enhancement of the radial magnetic field from Rayleigh-Taylor instabilities will also extend all the way to the shock front, and this may help explain the slight dominance of radial fields long seen in polarization measurements of young remnants like Tycho.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Blondin, JM and Ellison, DC}, year={2001}, month={Oct}, pages={244–253} }
 @article{boroson_kallman_blondin_owen_2001, title={Testing hydrodynamic models of LMC X-4 with ultraviolet and X-ray spectra}, volume={550}, ISSN={["0004-637X"]}, DOI={10.1086/319773}, abstractNote={We compare the predictions of hydrodynamic models of the LMC X-4 X-ray binary system with observations of UV P Cygni lines with the Goddard High Resolution Spectrograph and Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The hydrodynamic model determines density and velocity fields of the stellar wind, wind-compressed disk, accretion stream, Keplerian accretion disk, and accretion disk wind. We use a Monte Carlo code to determine the UV P Cygni line profiles by simulating the radiative transfer of UV photons that originate on the star and are scattered in the wind. The qualitative orbital variation predicted is similar to that observed, although the model fails to reproduce the strong orbital asymmetry (the observed absorption is strongest for ϕ > 0.5). The model predicts a mideclipse X-ray spectrum, caused almost entirely by Compton scattering, with a factor of 4 less flux than observed with ASCA. We discuss how the model may need to be altered to explain the spectral variability of the system.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Boroson, B and Kallman, T and Blondin, JM and Owen, MP}, year={2001}, month={Apr}, pages={919–930} }
 @article{pereyra_kallman_blondin_2000, title={Hydrodynamic models of line-driven accretion disk winds. II. Adiabatic winds from nonisothermal disks}, volume={532}, ISSN={["0004-637X"]}, DOI={10.1086/308527}, abstractNote={We present here numerical hydrodynamic simulations of line-driven accretion disk winds in cataclysmic variable systems. We calculate wind mass-loss rate, terminal velocities, and line profiles for C IV (1550 Å) for various viewing angles. The models are 2.5-dimensional, include an energy balance condition, and calculate the radiation field as a function of position near an optically thick accretion disk. The model results show that centrifugal forces produce collisions of streamlines in the disk wind that in turn generate an enhanced density region, underlining the necessity of two-dimensional calculations where these forces may be represented. For disk luminosity Ldisk = L☉, white dwarf mass Mwd = 0.6 M☉, and white dwarf radii Rwd = 0.01 R☉, we obtain a wind mass-loss rate of wind = 8 × 10-12 M☉ yr-1, and a terminal velocity of ~3000 km s-1. The line profiles we obtain are consistent with observations in their general form, in particular in the maximum absorption at roughly half the terminal velocity for the blueshifted component, in the magnitudes of the wind velocities implied by the absorption components, in the FWHM of the emission components, and in the strong dependence in inclination angle.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Pereyra, NA and Kallman, TR and Blondin, JM}, year={2000}, month={Mar}, pages={563–580} }
 @article{blondin_2000, title={Tidally-driven transport in accretion disks in close binary systems}, volume={5}, ISSN={["1384-1092"]}, DOI={10.1016/S1384-1076(00)00006-3}, abstractNote={The effects of binary tidal forces on transport within an accretion disk are studied with a time-dependent hydrodynamical model of a two-dimensional isothermal accretion disk. Tidal forces quickly truncate the accretion disk to radii of order half the average radius of the Roche lobe, and excite a two-armed spiral wave that remains stationary in the rotating reference frame of the binary system. We measure an effective α of order 0.1 near the outer edge of the disk in all of our models, independent of the mass ratio of the binary system, the Mach number of the orbital motion in the disk, and the radial density profile of the disk. The value of α drops with decreasing radius, implying that steady-state models (constant mass accretion rate at all radii) do not exist. In cold disks with high Mach number, the effective α drops so rapidly that it falls below our threshold of measurement (∼10−3) at a radius of only one third the tidal radius. In warmer disks where the Mach numbers remain below 20, we can measure an effective α down to radii 10 times smaller than the maximum size of the disk.}, number={1}, journal={NEW ASTRONOMY}, publisher={Elsevier BV}, author={Blondin, JM}, year={2000}, month={Mar}, pages={53–68} }
 @article{mezzacappa_calder_bruenn_blondin_guidry_strayer_umar_1998, title={An investigation of neutrino-driven convection and the core collapse supernova mechanism using multigroup neutrino transport}, volume={495}, ISSN={["0004-637X"]}, DOI={10.1086/305338}, abstractNote={We investigate neutrino-driven convection in core collapse supernovae and its ramifications for the explosion mechanism. We begin with a postbounce model that is optimistic in two important respects: (1) we begin with a 15 M☉ precollapse model, which is representative of the class of stars with compact iron cores; (2) we implement Newtonian gravity. Our precollapse model is evolved through core collapse and bounce in one dimension using multigroup (neutrino energy-dependent) flux-limited diffusion (MGFLD) neutrino transport and Newtonian Lagrangian hydrodynamics, providing realistic initial conditions for the postbounce convection and evolution. Our two-dimensional simulation begins at 12 ms after bounce and proceeds for 500 ms. We couple two-dimensional piecewise parabolic method (PPM) hydrodynamics to precalculated one-dimensional MGFLD neutrino transport. (The neutrino distributions used for matter heating and deleptonization in our two-dimensional run are obtained from an accompanying one-dimensional simulation. The accuracy of this approximation is assessed.) For the moment, we sacrifice dimensionality for realism in other aspects of our neutrino transport. MGFLD is an implementation of neutrino transport that simultaneously (1) is multigroup and (2) simulates with sufficient realism the transport of neutrinos in opaque, semitransparent, and transparent regions. Both are crucial to the accurate determination of postshock neutrino heating, which sensitively depends on the luminosities, spectra, and flux factors of the electron neutrinos and antineutrinos emerging from their respective neutrinospheres. By 137 ms after bounce, we see neutrino-driven convection rapidly developing beneath the shock. By 212 ms after bounce, this convection becomes large scale, characterized by higher entropy, expanding upflows and lower entropy, denser, finger-like downflows. The upflows reach the shock and distort it from sphericity. The radial convection velocities at this time become supersonic just below the shock, reaching magnitudes in excess of 109 cm s-1. Eventually, however, the shock recedes to smaller radii, and at ~500 ms after bounce there is no evidence in our simulation of an explosion or of a developing explosion. Our angle-averaged density, entropy, electron fraction, and radial velocity profiles in our two-dimensional model agree well with their counterparts in our accompanying one-dimensional MGFLD run above and below the neutrino-driven convection region. In the convection region, the one-dimensional and angle-averaged profiles differ somewhat because (1) convection tends to flatten the density, entropy, and electron fraction profiles, and (2) the shock radius is boosted somewhat by convection. However, the differences are not significant, indicating that, while vigorous, neutrino-driven convection in our model does not have a significant impact on the overall shock dynamics. The differences between our results and those of other groups are considered. These most likely result from differences in (1) numerical hydrodynamics methods; (2) initial postbounce models, and, most important; (3) neutrino transport approximations. We have compared our neutrino luminosities, rms energies, and inverse flux factors with those from the exploding models of other groups. Above all, we find that the neutrino rms energies computed by our multigroup (MGFLD) transport are significantly lower than the values obtained by Burrows and coworkers, who specified their neutrino spectra by tying the neutrino temperature to the matter temperature at the neutrinosphere and by choosing the neutrino degeneracy parameter arbitrarily, and by Herant and coworkers in their transport scheme, which (1) is gray and (2) patches together optically thick and thin regions. The most dramatic difference between our results and those of Janka and Müller is exhibited by the difference in the net cooling rate below the gain radii: Our rate is 2-3 times greater during the critical 50-100 ms after bounce. We have computed the mass and internal energy in the gain region as a function of time. Up to ~150 ms after bounce, we find that both increase as a result of the increasing gain region volume, as the gain and shock radii diverge. However, at all subsequent times, we find that the mass and internal energy in the gain region decrease with time in accordance with the density falloff in the preshock region and with the flow of matter into the gain region at the shock and out of the gain region at the gain radius. Therefore, we see no evidence in the simulations presented here that neutrino-driven convection leads to mass and energy accumulation in the gain region. We have compared our one- and two-dimensional densities, temperatures, and electron fractions in the region below the electron neutrino and antineutrino gain radii, above which the neutrino luminosities are essentially constant (i.e., the neutrino sources are entirely enclosed), in an effort to assess how spherically symmetric our neutrino sources remain during our two-dimensional evolution, and therefore, in an effort to assess our use of precalculated one-dimensional MGFLD neutrino distributions in calculating the matter heating and deleptonization. We find no difference below the neutrinosphere radii. Between the neutrinosphere and gain radii we find no differences with obvious ramifications for the supernova outcome. We note that the interplay between neutrino transport and convection below the neutrinospheres is a delicate matter and is discussed at greater length in another paper (Mezzacappa and coworkers). However, the results presented therein do support our use of precalculated one-dimensional MGFLD in the present context. Failure in our "optimistic" 15 M☉ Newtonian model leads us to conclude that it is unlikely, at least in our approximation, that neutrino-driven convection will lead to explosions for more massive stars with fatter iron cores or in cases in which general relativity is included.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Mezzacappa, A and Calder, AC and Bruenn, SW and Blondin, JM and Guidry, MW and Strayer, MR and Umar, AS}, year={1998}, month={Mar}, pages={911-+} }
 @article{pereyra_kallman_blondin_1998, title={Hydrodynamic models of line-driven accretion disk winds in cataclysmic variables}, DOI={10.1063/1.55934}, abstractNote={We present one-dimensional isothermal analytic hydrodynamic models, both one-dimensional and two-dimensional isothermal numerical models, and two-dimensional adiabatic alpha disk numerical models for line-driven accretion disk winds from CVs. Using the one-dimensional analytic models we explore the physical conditions necessary for the existence of a disk wind. Using the two-dimensional isothermal model we explore the effects of centrifugal forces in the wind, and show that these forces cause the wind stream lines to collide producing enhanced density regions in the disk wind. For disk luminosity Ldisk=L⊙, white dwarf mass Mwd=0.6M⊙, and white dwarf radii Rwd=0.01R⊙, through the two-dimensional adiabatic alpha disk model we obtain a wind mass-loss rate of 8×10−12M⊙ yr−1, a terminal velocity of ∼3000 km s−1, and line profiles for CIV (1550 A) for various angles. The line profiles obtained are consistent with observations in their general form and strong dependence in inclination angle. Thus we are able to ...}, journal={AIP Conference Proceedings}, publisher={AIP}, author={Pereyra, N. A. and Kallman, T. R. and Blondin, J. M.}, year={1998} }
 @article{blondin_koerwer_1998, title={Instability of isothermal stellar wind bowshocks}, volume={3}, ISSN={["1384-1092"]}, DOI={10.1016/S1384-1076(98)00028-1}, abstractNote={We present hydrodynamical simulations illustrating the instability of stellar wind bowshocks in the limit of an isothermal equation of state. In this limit, the bowshock is characterized by a thin dense shell bounded on both sides by shocks. In a time-averaged sense the shape of this bowshock shell roughly matches the steady state solution of Wilkin (1996)[ApJ, 459, L31], although the apex of the bowshock can deviate in or out by a factor of two or more. The shape of the bowshock is distorted by large amplitude kinks with a characteristic wavelength of order the standoff distance from the star. The instability is driven by a strong shear flow within the shock-bounded shell, suggesting an origin related to the nonlinear thin-shell instability. This instability occurs when both the forward bowshock and the reverse wind shock are effectively isothermal and the star is moving through the interstellar medium with a Mach number greater than a few. This work therefore suggests that ragged, clumpy bowshocks should be expected to surround stars with a slow, dense wind (which leads to rapid cooling behind the reverse wind shock), whose velocity with respect to the surrounding interstellar medium is of order 60kms−1 (leading both to rapid cooling behind the forward bowshock and sufficiently high Mach numbers to drive the instability).}, number={8}, journal={NEW ASTRONOMY}, publisher={Elsevier BV}, author={Blondin, JM and Koerwer, JF}, year={1998}, month={Oct}, pages={571–582} }
 @article{mezzacappa_calder_bruenn_blondin_guidry_strayer_umar_1998, title={The interplay between proto-neutron star convection and neutrino transport in core-collapse supernovae}, volume={493}, ISSN={["0004-637X"]}, DOI={10.1086/305164}, abstractNote={We couple two-dimensional hydrodynamics to realistic one-dimensional multigroup flux-limited diffusion neutrino transport to investigate proto-neutron star convection in core-collapse supernovae, and more specifically, the interplay between its development and neutrino transport. Our initial conditions, time-dependent boundary conditions, and neutrino distributions for computing neutrino heating, cooling, and deleptonization rates are obtained from one-dimensional simulations that implement multigroup flux-limited diffusion and one-dimensional hydrodynamics. The development and evolution of proto-neutron star convection are investigated for both 15 and 25 M☉ models, representative of the two classes of stars with compact and extended iron cores, respectively. For both models, in the absence of neutrino transport, the angle-averaged radial and angular convection velocities in the initial Ledoux unstable region below the shock after bounce achieve their peak values in ~20 ms, after which they decrease as the convection in this region dissipates. The dissipation occurs as the gradients are smoothed out by convection. This initial proto-neutron star convection episode seeds additional convectively unstable regions farther out beneath the shock. The additional proto-neutron star convection is driven by successive negative entropy gradients that develop as the shock, in propagating out after core bounce, is successively strengthened and weakened by the oscillating inner core. The convection beneath the shock distorts its sphericity, but on the average the shock radius is not boosted significantly relative to its radius in our corresponding one-dimensional models. In the presence of neutrino transport, proto-neutron star convection velocities are too small relative to bulk inflow velocities to result in any significant convective transport of entropy and leptons. This is evident in our two-dimensional entropy snapshots, which in this case appear spherically symmetric. The peak angle-averaged radial and angular convection velocities are orders of magnitude smaller than they are in the corresponding "hydrodynamics-only" models. A simple analytical model supports our numerical results, indicating that the inclusion of neutrino transport reduces the entropy-driven (lepton-driven) convection growth rates and asymptotic velocities by a factor ~3 (50) at the neutrinosphere and a factor ~250 (1000) at ρ = 1012 g cm-3, for both our 15 and 25 M☉ models. Moreover, when transport is included, the initial postbounce entropy gradient is smoothed out by neutrino diffusion, whereas the initial lepton gradient is maintained by electron capture and neutrino escape near the neutrinosphere. Despite the maintenance of the lepton gradient, proto-neutron star convection does not develop over the 100 ms duration typical of all our simulations, except in the instance where "low-test" intial conditions are used, which are generated by core-collapse and bounce simulations that neglect neutrino-electron scattering and ion-ion screening corrections to neutrino-nucleus elastic scattering. Models favoring the development of proto-neutron star convection either by starting with more favorable, albeit artificial (low-test), initial conditions or by including transport corrections that were ignored in our "fiducial" models were considered. Our conclusions nonetheless remained the same. Evidence of proto-neutron star convection in our two-dimensional entropy snapshots was minimal, and, as in our fiducial models, the angle-averaged convective velocities when neutrino transport was included remained orders of magnitude smaller than their counterparts in the corresponding hydrodynamics-only models.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Mezzacappa, A and Calder, AC and Bruenn, SW and Blondin, JM and Guidry, MW and Strayer, MR and Umar, AS}, year={1998}, month={Feb}, pages={848-+} }
 @article{blondin_wright_borkowski_reynolds_1998, title={Transition to the radiative phase in supernova remnants}, volume={500}, ISSN={["0004-637X"]}, DOI={10.1086/305708}, abstractNote={The evolution of a supernova remnant through the transition from an adiabatic Sedov-Taylor blast wave to a radiative pressure-driven snowplow phase is studied using one- and two-dimensional hydrodynamic simulations. This transition is marked by a catastrophic collapse of the postshock gas, forming a thin, dense shell behind the forward shock. After the transition, the shock front is characterized by a deceleration parameter, Vt/R ≈ 0.33, which is considerably higher than the analytic estimate of for a pressure-driven snowplow. In two dimensions, the catastrophic collapse is accompanied by violent dynamical instabilities of the thin, cool shell. The violence of the collapse and the subsequent instability of the shell increase with increasing ambient density. Preshock density perturbations as small as 1% in an ambient medium with density of 100 cm-3 can lead to distortions of the shock front larger than 10% of the radius of the remnant.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Blondin, JM and Wright, EB and Borkowski, KJ and Reynolds, SP}, year={1998}, month={Jun}, pages={342–354} }
 @article{borkowski_blondin_harrington_1997, title={Collimation of astrophysical jets: The proto-planetary nebula He 3-1475}, volume={482}, ISSN={["0004-637X"]}, DOI={10.1086/310679}, abstractNote={The proto-planetary nebula He 3-1475 was imaged in the [N II] λ6584 line with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. This image has revealed what appear to be large-scale flows being collimated into narrow bipolar jets. This is a unique object: we may be observing the actual collimation process of an astrophysical jet. Analytical models and hydrodynamical simulations suggest that the jet in He 3-1475 may be produced by purely hydrodynamical means, through focusing of a weakly collimated bipolar outflow into jets by oblique radiative shocks.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Borkowski, KJ and Blondin, JM and Harrington, JP}, year={1997}, month={Jun}, pages={L97-&} }
 @inproceedings{dwarkadas_chevalier_blondin_1997, title={Effect of ambient wind velocity on planetary nebula morphology}, volume={180}, DOI={10.1007/978-94-011-5244-0_81}, booktitle={Planetary nebulae: Proceedings of the 180th Symposium of the International Astronomical Union, held in Groningen, The Netherlands, August 26-30, 1996}, publisher={Boston, Mass.: Kluwer Academic Publishers, 1997}, author={Dwarkadas, V. V. and Chevalier, R. A. and Blondin, John}, editor={H. J. Habing and Lamers, H. J. G. L. M.Editors}, year={1997}, pages={224} }
 @article{blondin_marks_1997, title={Evolution of cold shock bounded slabs}, volume={1}, DOI={10.1016/s1384-1076(96)00019-x}, abstractNote={The stability and evolution of cold, shock-bounded slabs is studied using numerical hydrodynamic simulations. We confirm the analysis of Vishniac (1994) [ApJ, 428, 186], who showed that such slabs are unstable if they are perturbed by a displacement larger than their width. The growth rate of this nonlinear thin shell instability (NTSI) is found to increase with decreasing wavelength, in qualitative agreement with Vishniac's analysis. The NTSI saturates when the bending angle becomes large and the growth in the width of the slab pinches off the perturbation. After saturation, the slab remains greatly extended with an average density much less than the original slab density, supported primarily by supersonic turbulence within the slab. Linear perturbations are also found to be unstable in that they can lead to turbulent flow within the slab, although this response to linear perturbations is distinct from, and much less violent than the NTSI. Richard McCray}, number={3}, journal={New Astronomy}, author={Blondin, John and Marks, B. S.}, year={1997}, pages={235–244} }
 @article{pereyra_kallman_blondin_1997, title={Hydrodynamical Models of Line‐driven Accretion Disk Winds}, volume={477}, DOI={10.1086/303671}, abstractNote={We present here one-dimensional analytic hydrodynamic models and both one-dimensional and two-dimensional numerical hydrodynamic models for line-driven accretion disk winds from cataclysmic variable (CV) systems. Using the one-dimensional analytic models we explore the physical conditions necessary for the existence of a disk wind and study the dependence of wind speed and mass-loss rate on radius. The results of our two-dimensional model are consistent with the spectrum observed from CVs in the polar nature of the wind, the maximum absorption at roughly half the terminal speed of the P Cygni profiles, and the order of magnitude of the terminal speeds. For disk luminosity Ldisk = L☉, white dwarf mass Mwd = 0.6 M☉, disk radius Rdisk = R☉, and sound speed a = 10 km s-1 we obtain a wind mass-loss rate of Ṁwind=2 × 10−14 M yr-1 and a terminal velocity of ~3000 km s-1. The two-dimensional models show that centrifugal forces produce shocks in the disk wind. If these shocks were absent, the mass-loss rates obtained would be too low to produce the optical depths required to explain the P Cygni profile of CVs. The two-dimensional models demonstrate the importance of centrifugal forces in winds from accretion disks and thus the necessity of models where these forces may be represented.}, number={1}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Pereyra, Nicolas Antonio and Kallman, Timothy R. and Blondin, John M.}, year={1997}, month={Mar}, pages={368–378} }
 @article{layton_blondin_owen_stevens_1997, title={Tidal mass transfer in elliptical-orbit binary stars}, volume={3}, DOI={10.1016/s1384-1076(97)00047-x}, abstractNote={High mass X-ray binary star systems with elliptical orbits, like GX 301-2, often exhibit a peak in X-ray luminosity associated with periastron passage. We use a two dimensional hydrodynamics code to examine the possibility that these X-ray flares result from tidal stripping of gas from the primary star, and subsequent accretion of this gas onto the compact companion. We find that if the primary star is rotating near corotation with the orbiting compact companion at periastron, tidally stripped gas can accrete, causing X-ray flares. Such a tidally induced flare will occur substantially after periastron, at a phase of ∼ 0.2 for the parameters used in our model. This flare is characterized by a brief disk accretion phase with a large angular momentum accretion rate. However, in our particular model this disk accretion phase was followed by an equally brief phase of accretion with the opposite sign of angular momentum, resulting in no long-term spin up of the X-ray pulsar.}, number={2}, journal={New Astronomy}, author={Layton, J. T. and Blondin, John and Owen, M. P. and Stevens, I. R.}, year={1997}, pages={111–119} }
 @article{borkowski_blondin_mccray_1997, title={X-Ray and Ultraviolet Line Emission from SNR 1987A}, volume={476}, DOI={10.1086/310487}, abstractNote={The soft X-ray emission seen from SN 1987A and the apparent deceleration of the radio source expansion suggest that the supernova blast wave has encountered a moderately dense H II region interior to the inner circumstellar ring. We simulate the hydrodynamics of this interaction and calculate the resulting X-ray and ultraviolet emission-line spectrum and light curves. The soft X-ray spectrum is dominated by emission lines of hydrogenic and helium-like C, N, O, and Ne; it is consistent with the ROSAT observations if Fe is depleted on grains. N V λλ1240 emission should be observable easily with the Hubble Space Telescope. The blast wave should strike the inner circumstellar ring around A.D. 2007.}, number={1}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Borkowski, Kazimierz J. and Blondin, John M. and McCray, Richard}, year={1997}, month={Feb}, pages={L31–L34} }
 @article{borkowski_blondin_mccray_1997, title={X‐Rays from the Impact of SN 1987A with Its Circumstellar Ring}, volume={477}, DOI={10.1086/303691}, abstractNote={We present models for the hydrodynamics of the impact of the envelope of SN 1987A with its inner circumstellar ring and for the resulting X-ray spectra and light curves. If the impact begins in A.D. 2000, the X-rays should be bright enough to resolve several emission lines with spectrometers on-board AXAF and Astro-E; if it begins in A.D. 2005, the X-rays will be roughly an order of magnitude brighter and have harder spectra. We compare our results with those from previous models and provide scaling laws to extend our results to models with impact times and ring densities different from those presented here. Within a few years after impact, the X-rays will brighten and their spectra will harden, owing to a complex variation of temperature within the shocked ring caused by the merger of primary and reflected shocks. The impact will continue for decades, and the X-rays will steadily increase in luminosity and temperature as the shock enters heretofore unseen matter in the ring.}, number={1}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Borkowski, Kazimierz J. and Blondin, John M. and McCray, Richard}, year={1997}, month={Mar}, pages={281–293} }
 @article{borkowski_szymkowiak_blondin_sarazin_1996, title={A Circumstellar Shell Model for the Cassiopeia A Supernova Remnant}, volume={466}, DOI={10.1086/177560}, abstractNote={view Abstract Citations (63) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Circumstellar Shell Model for the Cassiopeia A Supernova Remnant Borkowski, Kazimierz ; Szymkowiak, Andrew E. ; Blondin, John M. ; Sarazin, Craig L. Abstract We model the Cassiopeia A supernova remnant in the framework of the circumstellar medium (C SM) interaction picture. In this model, the slow red supergiant wind of the supernova (SN) progenitor was swept into a dense shell by a fast stellar wind in the subsequent blue supergiant stage of the progenitor star. The supernova blast wave propagated quickly (≤ 100 yr) through the tenuous wind-blown bubble located within this shell and then slowed down in the dense (nH ∼15 cm-3) CSM shell. The shell was impulsively accelerated during this interaction stage; during the subsequent interaction with SN ejecta, the shell has been further accelerated to ∼2000 km s-1, the currently observed expansion rate. The comparison of our X-ray emission calculations with the ASCA spectrum suggests that about 8 Msun of X- material is present in Cas A. Most of this mass is located in the CSM shell and in the outlying red supergiant wind. The X-ray continuum and the Fe Kα line are dominated by the shell emission, but prominent Kα complexes of Mg, Si, and S must be produced by SN ejecta with strongly enhanced abundances of these elements. Our hydrodynamical models indicate that about 2 Msun of ejecta have been shocked. An explosion of a stellar He core is consistent with these findings. Publication: The Astrophysical Journal Pub Date: August 1996 DOI: 10.1086/177560 Bibcode: 1996ApJ...466..866B Keywords: ISM: SUPERNOVA REMNANTS; HYDRODYNAMICS; ISM: INDIVIDUAL NAME: CASSIOPEIA A; STARS: CIRCUMSTELLAR MATTER full text sources ADS | data products SIMBAD (1) HEASARC (1)}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Borkowski, Kazimierz and Szymkowiak, Andrew E. and Blondin, John M. and Sarazin, Craig L.}, year={1996}, month={Aug}, pages={866} }
 @article{blondin_lundqvist_chevalier_1996, title={Axisymmetric Circumstellar Interaction in Supernovae}, volume={472}, DOI={10.1086/178060}, abstractNote={Multiwavelength observations of Type II supernovae have shown evidence of the interaction between supernovae and the dense slow winds from the red supergiant progenitor stars. Observations of planetary nebulae and the nebula around SN 1987A show that the slow winds from extended stars frequently have an axisymmetric structure with a high density in the equatorial plane. We have carried out numerical calculations of the interaction of a supernova with such an axisymmetric density distribution. For small values of the angular density gradient at the pole, the asymmetry in the interaction shell is greater than, but close to, that expected from purely radial motion. If the angular density gradient is above a moderate value, then the flow qualitatively changes and a protrusion emerges along the axis. For a power-law supernova density profile, the flow approaches a self-similar state in which the protrusion length is 2–4 times the radius of the main shell. The critical density gradient is larger for steeper density profiles of the ejecta. Most of our calculations are axisymmetric, but we have carried out a three-dimensional calculation to show that the protrusion is not a numerical artifact along the symmetry axis. For typical supernova parameters, the protrusions take ≳ several years to develop. The appearance of the shell with protrusions is similar to that observed in VLBI radio images of the remnant 41.9+58 in M82 and possibly of SN 1986J. We also considered the possibility of asymmetric ejecta and found that it had a relatively small effect on the asymmetry of the interaction region.}, number={1}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Lundqvist, Peter and Chevalier, Roger A.}, year={1996}, month={Nov}, pages={257–266} }
 @article{dwarkadas_chevalier_blondin_1996, title={The Shaping of Planetary Nebulae: Asymmetry in the External Wind}, volume={457}, DOI={10.1086/176772}, abstractNote={view Abstract Citations (51) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Shaping of Planetary Nebulae: Asymmetry in the External Wind Dwarkadas, Vikram V. ; Chevalier, Roger A. ; Blondin, John M. Abstract We have modeled planetary nebulae (PNs) in the context of the interacting stellar winds model. If the two interacting winds have constant properties, the velocity of the PN shell tends toward a constant with time and the shape becomes self-similar. Additionally, if the velocity of the fast wind is much higher than the expansion velocity of the shell, the interior of the hot shocked bubble becomes isobaric. Using semi-analytical methods, complemented by hydrodynamic simulations, we have calculated the shapes of PNs in the self-similar stage. An asymmetric density profile is assumed for the slow outer wind. The asymmetry is modeled using different functions, which depend on the degree of asymmetry and the steepness of the density profile in the angular direction. We include the effects of the ambient wind velocity, which has not received much attention since the work of Kahn & West (1985). The fact that typical PN velocities (10-40 km s-1) are only marginally greater than typical red giant wind velocities (5-20 km s-1) indicates that this is an important parameter. The morphological appearance is a consequence of the density contrast, steepness of the density profile and velocity of the ambient medium; classification of PNs purely on the basis of the first two factors may be misleading. Moderate values of the density contrast result in a cusp at the equator. A higher density contrast coupled with a low velocity for the external medium gives rise to extremely bipolar nebulae. For large density contrasts and a significant value of the slow wind velocity, the surface density maximum of the shell shifts away from the equator, giving rise to peanut-shaped structures with pronounced equatorial bulges. If the external wind velocity is small compared to the expansion velocity of the nebula, the PNs tend to be more bipolar, even with a moderate density contrast. If the PN velocity is close to that of the external wind, the shape is relatively spherical. However, a velocity asymmetry in the external wind can lead to a bipolar shape if the equatorial velocity is sufficiently low. Our numerical simulations show that asymmetric PN shells are corrugated because of Kelvin-Helmholtz instabilities. They also indicate that several doubling times are needed to approach the self-similar state. A ratio of interior sound speed to shell velocity ≳10 is found to yield nebulae whose shapes match those given by the isobaric approximation. Publication: The Astrophysical Journal Pub Date: February 1996 DOI: 10.1086/176772 Bibcode: 1996ApJ...457..773D Keywords: HYDRODYNAMICS; ISM: BUBBLES; ISM: STRUCTURE; ISM: PLANETARY NEBULAE: GENERAL; STARS: MASS LOSS full text sources ADS | data products SIMBAD (12)}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Dwarkadas, Vikram V. and Chevalier, Roger A. and Blondin, John M.}, year={1996}, month={Feb}, pages={773} }
 @article{chevalier_blondin_1995, title={Hydrodynamic instabilities in supernova remnants: Early radiative cooling}, volume={444}, DOI={10.1086/175606}, abstractNote={view Abstract Citations (93) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hydrodynamic Instabilities in Supernova Remnants: Early Radiative Cooling Chevalier, Roger ; Blondin, John M. Abstract The initial interaction of a supernova with its surrounding medium gives rise to a double shell structure bounded by shock waves, in which the deceleration of the supernova gas is subject to hydrodynamic instabilities. For the case where the surrounding medium is a circumstellar wind, the high density at early times can give rise to radiative cooling of the shocked supernova gas, in which case the shocked supernova gas forms a very thin shell. We analyze the instability in the thin shell approximation and find an expression for the linear growth rate that can be compared to results from adiabatic calculations. For perturbed wavelengths that are larger than the adiabatic supernova shell thickness, there is excellent agreement between the two growth rates; at smaller wavelengths, the thin shell growth rate becomes larger than that in the adiabatic case. The results show that the thin shell analysis incorporates the salient physical situation for the instability. Numerical simulations confirm the instability analysis in the linear regime and allow the instability to be studied in the nonlinear regime. With radiative cooling, the instability saturates at an amplitude comparable to that found for the adiabatic case - at about half the shell thickness for one case. It appears that once the density contrast becomes large, the outcome of the instability no longer depends on the density contrast. The importance of the instability for radio supernovae is that cool, partially ionized gas is mixed into the region that may give rise to radio synchrotron emission. The resulting free-free absorption may be a factor in the turn-on of radio supernovae. Variations in the shell column density around the shocked shell can be a factor in the absorption of X-rays from the reverse shock front. The clumpiness can also give fluctuations in the emission-line profiles of shocked ejecta gas. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175606 Bibcode: 1995ApJ...444..312C Keywords: Hydrodynamics; Radiant Cooling; Shells (Structural Forms); Shock Waves; Stability; Stellar Envelopes; Supernova Remnants; Perturbation; Simulation; Stellar Mass Ejection; Stellar Winds; Astrophysics; HYDRODYNAMICS; INSTABILITIES; SHOCK WAVES; STARS: SUPERNOVAE: GENERAL full text sources ADS | data products SIMBAD (4)}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Chevalier, Roger and Blondin, John M.}, year={1995}, month={May}, pages={312} }
 @article{blondin_richards_malinowski_1995, title={Hydrodynamic simulations of the mass transfer in Algol}, volume={445}, DOI={10.1086/175753}, abstractNote={view Abstract Citations (42) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hydrodynamic Simulations of the Mass Transfer in Algol Blondin, John M. ; Richards, Mercedes T. ; Malinowski, Michael L. Abstract We have conducted two-dimensional hydrodynamic simulations of the mass transfer of the short-period binary Algol (beta Persei). Optical H alpha line observations suggest that the Algol system possesses a transient accretion disk, in contrast to long-period systems in which a steady accretion disk is inferred. We have used our model to explore the dependence of the circumstellar flow on three parameters: the velocity, angle, and density of the tidal stream of gas flowing from the evolved companion star toward the more massive main-sequence star. The flow is relatively insensitive to the initial speed and direction of the tidal stream, but varies substantially depending on the density of the stream. For high values of the stream density, ns is greater than or approximately 109/cu cm, the gas is effectively isothermal and does not bounce off the surface of the primary star. For low values of the stream density, ns is less than or approximately 108/cu cm, the gas is effectively adiabatic and the high thermal pressure generated when the stream strikes the stellar results in an extended accretion disk. In the intermediate range of stream density, radiative cooling is only partially effective, and the tidal stream produces a variable accretion disk reminiscent of the transient accretion disk suggested by the optical observations. In all of our simulations the region of highest thermal pressure corresponded to the region of interaction between the gas stream from the secondary and the gas which had circled the primary star. This interaction region near the surface of the primary star at the line of centers may be the source of the localized H alpha emission observed in Algol. Publication: The Astrophysical Journal Pub Date: June 1995 DOI: 10.1086/175753 Bibcode: 1995ApJ...445..939B Keywords: Accretion Disks; Eclipsing Binary Stars; Hydrodynamic Equations; Mass Transfer; Stellar Envelopes; Two Dimensional Models; Cooling; Gas Flow; H Alpha Line; Radiative Transfer; X Ray Spectra; Astrophysics; ACCRETION; ACCRETION DISKS; HYDRODYNAMICS; STARS: BINARIES: ECLIPSING; STARS: CIRCUMSTELLAR MATTER; STARS: INDIVIDUAL CONSTELLATION NAME: BETA PERSEI full text sources ADS | data products SIMBAD (2)}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Richards, Mercedes T. and Malinowski, Michael L.}, year={1995}, month={Jun}, pages={939} }
 @article{strickland_blondin_1995, title={Numerical Analysis of the Dynamic Stability of Radiative Shocks}, volume={449}, DOI={10.1086/176093}, abstractNote={view Abstract Citations (69) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Numerical Analysis of the Dynamic Stability of Radiative Shocks Strickland, Russell ; Blondin, John M. Abstract Radiative shocks perturbed from steady state are subject to an oscillatory overstability. We have examined the nature of this overstability in one and two dimensions using numerical hydrodynamic simulations. We find that one-dimensional simulations of a uniform flow incident upon a reflecting wall produce oscillation frequencies in agreement with those of earlier analytic (Chevalier & Imamura 1982) and numerical (Imamura, Wolff, & Durisen 1984) work. We do not, however, find any evidence for positive growth rates. This result is not in contradiction with previous linear analysis because the supersonic flow into a wall problem is at a saturated, nonlinear amplitude from the beginning. In the case of one-dimensional steady state shocks in the absence of a solid wall, we find a slightly different dependence of the overstability on α when we assume a cooling rate proportional to Tα. In this case oscillations in radiative shocks with α ≲ 0.75 are found to saturate at a finite amplitude, i.e., the relevant critical value of alpha is at least above 0.5. We also find high Mach number systems to be less stable than low Mach number systems subject to the same cooling law. Simulations of two-dimensional steady state shocks reveal that transverse perturbations in the shock front quickly manifest themselves in the cold, dense gas layer downstream of the cooling region. Perturbations in the cold gas layer are dominated by spatial wavelengths, λ ≲ Lc, the cooling length of the shock. The action of this instability ensures that interstellar radiative shocks will not be smooth on length scales of order the local cooling length. Publication: The Astrophysical Journal Pub Date: August 1995 DOI: 10.1086/176093 Bibcode: 1995ApJ...449..727S Keywords: HYDRODYNAMICS; INSTABILITIES; METHODS: NUMERICAL; SHOCK WAVES full text sources ADS |}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Strickland, Russell and Blondin, John M.}, year={1995}, month={Aug}, pages={727} }
 @article{blondin_woo_1995, title={Wind dynamics in SMC X-1. 1: Hydrodynamic simulation}, volume={445}, DOI={10.1086/175748}, abstractNote={We present a three-dimensional hydrodynamic simulation of the disrupted stellar wind in the high-mass X-ray binary system SMC X-1. The three dominant processes that determine the geometry of the wind in high X-ray luminosity systems such as SMC X-1 are the X-ray suppression of the stellar wind from the X-ray irradiated face of the primary star, the focusing of the radiatively driven wind in the X-ray shadow by the effects of stellar rotation, and the rapid X-ray heating of gas in the vicinity of the X-ray source, including the X-ray illuminated surface of the primary star. The resulting distribution of circumstellar gas provides a successful explanation for the asymmetric, extended eclipse transitions and the intensity of the deep eclipse X-ray emission in SMC X-1, as well as a possible explanation for the X-ray dips seen near superior conjunction of the X-ray source in Cyg X-1.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Woo, Jonathan W.}, year={1995}, month={Jun}, pages={889} }
 @article{woo_clark_blondin_kallman_nagase_1995, title={Wind dynamics in SMC X-1. 2: GINGA and ROSAT observations}, volume={445}, DOI={10.1086/175749}, abstractNote={The X-ray phenomena of the binary system SMC X-1/Sk 160, observed with the Ginga and ROSAT X-ray observatories, are compared with computed phenomena derived from a three-dimensional hydrodynamical model of the stellar wind perturbed by X-ray heating and ionization which is described in the accompanying paper (Blondin & Woo 1995). In the model the B0 I primary star has a line-driven stellar wind in the region of the X-ray shadow and a thermal wind in the region heated by X-rays. We find general agreement between the observed and predicted X-ray spectrum throughout the binary orbit cycle, including the extended, variable, and asymmetric eclipse transitions and the period of deep eclipse.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Woo, Jonathan W. and Clark, George W. and Blondin, John M. and Kallman, Timothy R. and Nagase, Fumiaki}, year={1995}, month={Jun}, pages={896} }
 @article{borkowski_sarazin_blondin_1994, title={On the X-ray spectrum of Kepler's supernova remnant}, volume={429}, DOI={10.1086/174355}, abstractNote={We have devised a method to do nonequilibrium ionization calculations on the results of two-dimensional hydrodynamical simulations, based on the algorithm of Hughes & Helfand (1985). We have calculated the ionization structure and X-ray emission for a two-dimensional numerical hydrodynamical simulation for the remnant of Kepler's supernova (SN); the hydrodynamical model was presented in a previous paper. In this model, the progenitor of Kepler's SN is assumed to have been a massive runaway star ejected from the Galactic plane. In its red supergiant stage, its dense stellar wind was distorted and compressed into a bow shock by the ram pressure of the tenuous interstellar medium. The subsequent interaction of the supernova ejecta with this asymmetric circumstellar matter produced a strongly asymmetric supernova remnant (SNR). In this paper, we present calculated X-ray spectra for this hydrodynamical model. A comparison with observations implies a moderate overabundance of Fe in Kepler's SNR (only 50% larger than its cosmic value), in contrast to a large (6 to 15) Fe overabundance derived previously. However, we confirm earlier conclusions that Si and S abundances are 2 to 3 times solar. These modest enhancements of Si, S, and Fe may be attributed either to heavy-element enriched SN ejecta or to the initial chemical abundances of the SN progenitor, which originated in the metal-rich inner Galaxy. The comparison of our models with the observed spectra confirm theoretical predictions that moderate electron heating occurs at strong collisionless shock fronts, with the implied electron/mean temperature ratio of approximately 0.5.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Borkowski, Kazimierz J. and Sarazin, Craig L. and Blondin, John M.}, year={1994}, month={Jul}, pages={710} }
 @article{blondin_1994, title={SN progenitor winds}, DOI={10.1017/cbo9780511564628.018}, abstractNote={The conventional wisdom that a Type II supernova explosion occurs inside a spherical stellar wind bubble blown by the wind of the red supergiant progenitor misses two important points: the progenitor wind may be time-dependent, and it may be asymmetric. These two features of SN progenitor winds have been well illustrated by the ring observed around SN 1987A. The existence of this circumstellar shell directly implies a time-dependence in the wind on time scales less than about 10,000 years. Also, the shell is undeniably asymmetric, implying some form of asymmetry in the progenitor wind(s). Some of the theories for an asymmetric circumstellar medium include gravitational focussing in a wide binary, rotationally deformed wind, colliding winds in a binary system, and asymmetric mass ejection in a common envelope or accretion phase of a close binary system. The wind dynamics of these various theories will be reviewed with an eye toward understanding the true history of Sk -69°202.}, journal={Circumstellar Media in Late Stages of Stellar Evolution}, publisher={Cambridge University Press}, author={Blondin, John M.}, year={1994}, month={Aug}, pages={139–147} }
 @article{blondin_1994, title={The shadow wind in high-mass X-ray binaries}, volume={435}, DOI={10.1086/174853}, abstractNote={We present hydrodynamic simulations of the most X-ray luminous high-mass X-ray binary systems, such as Cen X-3 and SMC X-1. These models illustrate the presence of both a normal radiatively driven wind confined to the X-ray shadow of the primary star -- a shadow wind -- and a thermally driven wind excited by the X-ray heating of the primary's stellar surface -- an X-ray-excited wind. The X-ray flux in these systems is sufficiently intense that any circumstellar gas exposed to the X-ray source will be highly photoionized. These extreme ionization conditions prevent the formation of a normal radiatively driven wind from the irradiated surface of the primary, but such a wind can still form on the shadowed side of the primary. Orbital rotation can then bring this shadow wind into the line of sight toward the X-ray source, enhancing the column density of the wind seen near eclipse egress. Furthermore, such a high X-ray flux can also excite a thermal wind from the irradiated surface of the primary. Again, orbital rotation tends to deflect the wind, this time leading to an enhanced column density near eclipse ingress.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M.}, year={1994}, month={Nov}, pages={756} }
 @article{owocki_cranmer_blondin_1994, title={Two-dimensional hydrodynamical simulations of wind-compressed disks around rapidly rotating B stars}, volume={424}, DOI={10.1086/173938}, abstractNote={We use a 2-D PPM code to simulate numerically the hydrodynamics of a radiation-driven stellar wind from a rapidly rotating Be-star. The results generally confirm predictions of the semi-analytic “Wind Compressed Disk” model recently proposed by Bjorkman and Cassinelli to explain the cir­cumstellar disks inferred observationally to exist around such rapidly rotat­ing stars. However, this numerical simulation is able to incorporate several important effects not accounted for in the simple model, including a dynam­ical treatment of the outward radiative driving and gas pressure, as well as a rotationally oblated stellar surface. This enables us to model quantitatively the compressed wind and shock that forms the equatorial disk. The sim­ulation results thus do differ in several important details from the simple model, showing, for example, cases of inner disk inflow not possible in the heuristic approach of assuming a fixed outward velocity law. In addition, the disk opening typically has a half-angle of 2–4 degrees, somewhat larger than the ∼ 0.5° predicted from the analytic model, and there is no evidence for the predicted detachment of the disk that arises in the fixed outflow picture.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Owocki, Stanley P. and Cranmer, Steven R. and Blondin, John M.}, year={1994}, month={Apr}, pages={887} }
 @article{murray_white_blondin_lin_1993, title={Dynamical instabilities in two-phase media and the minimum masses of stellar systems}, volume={407}, DOI={10.1086/172540}, abstractNote={Two-phase media, with cool dense clouds in pressure equilibrium with a hot, tenuous background from which they have cooled, have a prominent place in astrophysics, possibly being involved in the evolution of cooling flows, active galactic nuclei, and the formation of galaxies, star clusters and individual stars. Following their formation, the cool clouds are subject to Kelvin-Helmholtz instability, which grows as they move through the background gas. The instability is suppressed if the clouds are bound by a sufficiently strong gravitational potential. Analytical estimates of the growth and stability requirements of clouds are presented and are compared with the results of two-dimensional hydrodynamical simulations}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Murray, Stephen D. and White, Simon D. M. and Blondin, John M. and Lin, Douglas N. C.}, year={1993}, month={Apr}, pages={588} }
 @article{blondin_lundqvist_1993, title={Formation of the circumstellar shell around SN 1987A}, volume={405}, DOI={10.1086/172366}, abstractNote={The nebulosity within a few arcseconds from SN 1987A has been modeled in terms of the supernova progenitor's fast wind interacting with a slow, asymmetric, previously emitted red supergiant wind. Previous models have relied on the assumption that the shocked blue supergiant wind is isobaric. We show that this approximation is unsatisfactory, and present two-dimensional time-dependent hydrodynamic calculations of the colliding winds model. From adiabatic models it is found that a ratio of equatorial to polar mass-loss rate during the red supergiant stage of at least ∼20 is needed to explain the observed structure. It is shown that not only this ratio, but also the form of polar dependence on asymmetry, is important to the formation of a compact ring structure}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Lundqvist, Peter}, year={1993}, month={Mar}, pages={337} }
 @article{blondin_lufkin_1993, title={The piecewise-parabolic method in curvilinear coordinates}, volume={88}, DOI={10.1086/191834}, abstractNote={We derive interpolation formulae for a third-order finite difference method in curvilinear, orthogonal coordinate systems. These formulae serve as a supplement to Colella and Woodward's PPM scheme for problems where the coordinate origin is included in the computational domain. Numerical examples of the improved accuracy of the advection scheme near coordinate singularities are shown.}, journal={The Astrophysical Journal Supplement Series}, publisher={IOP Publishing}, author={Blondin, John M. and Lufkin, Eric A.}, year={1993}, month={Oct}, pages={589} }
 @article{stevens_blondin_pollock_1992, title={Colliding winds from early-type stars in binary systems}, volume={386}, DOI={10.1086/171013}, abstractNote={The dynamics of the wind and shock structure formed by the wind collision in early-type binary systems is examined by means of a 2D hydrodynamics code, which self-consistently accounts for radiative cooling, and represents a significant improvement over previous attempts to model these systems. The X-ray luminosity and spectra of the shock-heated region, accounting for wind attenuation and the influence of different abundances on the resultant level and spectra of X-ray emission are calculated. A variety of dynamical instabilities that are found to dominate the intershock region is examined. These instabilities are found to be particularly important when postshock material is able to cool. These instabilities disrupt the postshock flow and add a time variability of order 10 percent to the X-ray luminosity. The X-ray spectrum of these systems is found to vary with the nuclear abundances of winds. These theoretical models are used to study several massive binary systems, in particular V444 Cyg and HD 193793.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Stevens, Ian R. and Blondin, John M. and Pollock, A. M. T.}, year={1992}, month={Feb}, pages={265} }
 @article{borkowski_blondin_sarazin_1992, title={Dynamics of Kepler's supernova remnant}, volume={400}, DOI={10.1086/171989}, abstractNote={Observations of Kepler's SNR have revealed a strong interaction with the ambient medium, far in excess of that expected at a distance of about 600 pc away from the Galactic plane where Kepler's SNR is located. This has been interpreted as a result of the interaction of supernova ejecta with the dense circumstellar medium (CSM). Based on the bow-shock model of Bandiera (1985), we study the dynamics of this interaction. The CSM distribution consists of an undisturbed stellar wind of a moving supernova progenitor and a dense shell formed in its interaction with a tenuous interstellar medium. Supernova ejecta drive a blast wave through the stellar wind which splits into the transmitted and reflected shocks upon hitting this bow-shock shell. We identify the transmitted shock with the nonradiative, Balmer-dominated shocks found recently in Kepler's SNR. The transmitted shock most probably penetrated the shell in the vicinity of the stagnation point.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Borkowski, Kazimierz J. and Blondin, John M. and Sarazin, Craig L.}, year={1992}, month={Nov}, pages={222} }
 @article{chevalier_blondin_emmering_1992, title={Hydrodynamic instabilities in supernova remnants - Self-similar driven waves}, volume={392}, DOI={10.1086/171411}, abstractNote={The initial interaction of a supernova with its surroundings involves the uniformly expanding, roughly power-law density profile of the outer parts. If the supernova gas has a steep power-law density profile and the surrounding density can be described by ρ ∞ r -s , with s = 0 for a uniform interstellar medium and s = 2 for a stellar wind, the interaction region is given by a self-similar solution. The profiles of the physical quantities in the shocked region show that the flow is subject to convective or Rayleigh-Taylor instability; the convective growth rate is largest at the contact discontinuity between the shocked supernova gas and the shocked surroundings}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Chevalier, Roger A. and Blondin, John M. and Emmering, Robert T.}, year={1992}, month={Jun}, pages={118} }
 @article{cioffi_blondin_1992, title={The evolution of cocoons surrounding light, extragalactic jets}, volume={392}, DOI={10.1086/171445}, abstractNote={If the mass density of supersonic, collimated material is less than that of the surrounding medium, a so-called light jet will be enveloped by a cocoon of overpressured shocked gas. Hydrodynamical simulations are used to understand the evolution of the cocoon. The cocoon's evolution is also compared to a simple analytic theory. To reconcile the theory with the simulations, the growth of the jet head must be taken into account. The overpressured cocoon stage exists for a relatively short astronomical time, after which only the region of the cocoon near the jet head remains overpressured. The spatial distribution of the optical emission often observed in distant extragalactic jet systems can be explained with this improved understanding of cocoon evolution.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Cioffi, Denis F. and Blondin, John M.}, year={1992}, month={Jun}, pages={458} }
 @article{blondin_stevens_kallman_1991, title={Enhanced winds and tidal streams in massive X-ray binaries}, volume={371}, DOI={10.1086/169934}, abstractNote={The tidal effects created by the presence of a compact companion are expected to induce a stream of enhanced wind from the early-type primary star in massive X-ray binary systems. In this paper, two-dimensional gasdynamical simulations of such streams are presented. It is found that the wind enhancement is a sensitive function of the binary separation, and develops into a tidal stream as the primary approaches its critical surface. For typical system parameters, the Coriolis force deflects the stream sufficiently that it does not impact directly on the compact companion but passes behind it. The density in the stream can reach values of 20-30 times the ambient wind density, leading to strong attenuation of the X-ray flux that passes through the tidal stream, providing a possible explanation of the enhanced absorption events seen at later phases in the X-ray observations of massive X-ray binary systems such as Vela X-1. In contrast to the time-variable accretion wake, the tidal stream is relatively stationary, producing absorption features that should remain fixed from orbit to orbit. For systems with a strong tidal stream, the large asymmetry in the accreting wind results in the accretion of angular momentum of constant sign, as opposed tomore » systems without streams, where the sign of the accreted angular momentum can change. 39 refs.« less}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Stevens, Ian R. and Kallman, Timothy R.}, year={1991}, month={Apr}, pages={684} }
 @article{blondin_kallman_fryxell_taam_1990, title={Hydrodynamic simulations of stellar wind disruption by a compact X-ray source}, volume={356}, DOI={10.1086/168865}, abstractNote={This paper presents two-dimensional numerical simulations of the gas flow in the orbital plane of a massive X-ray binary system, in which the mass accretion is fueled by a radiation-driven wind from an early-type companion star. These simulations are used to examine the role of the compact object (either a neutron star or a black hole) in disturbing the radiatively accelerating wind of the OB companion, with an emphasis on understanding the origin of the observed soft X-ray photoelectric absorption seen at late orbital phases in these systems. On the basis of these simulations, it is suggested that the phase-dependent photoelectric absorption seen in several of these systems can be explained by dense filaments of compressend gas formed in the nonsteady accreation bow shock and wake of the compact object. 61 refs.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Kallman, Timothy R. and Fryxell, Bruce A. and Taam, Ronald E.}, year={1990}, month={Jun}, pages={591} }
 @article{blondin_fryxell_konigl_1990, title={The structure and evolution of radiatively cooling jets}, volume={360}, DOI={10.1086/169128}, abstractNote={The two-dimensional simulations presently used to characterize the structure and evolution of radiatively cooling supersonic jets reveal that cooling jet morphologies resemble those of adiabatic outflows, but with the fundamental difference that a dense, cold shell will condense out of the shocked gas at the head of the jet when the cooling distance behind either of the two principal shocks is smaller than the jet radius. For very high cooling rates, the material that accumulates at the head of the jet forms an extended plug of cold gas resembling the nose cone observed in numerical simulations of strongly magnetized adiabatic jets. An investigation is made of the dependence of jet properties on the density ratio between the beam and the ambient medium, as well as on the strength of radiative cooling. 52 refs.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Fryxell, Bruce A. and Konigl, Arieh}, year={1990}, month={Sep}, pages={370} }
 @article{blondin_konigl_fryxell_1989, title={Herbig-Haro objects as the heads of radiative jets}, volume={337}, DOI={10.1086/185373}, abstractNote={The interpretation of certain HH objects as the heads of nonadiabatic supersonic jets is examined using two-dimensional numerical simulations. It is found that radiative jets develop a dense shell between the jet shock and the leading bow shock when the cooling distance behind either one of these shocks is smaller than the jet radius. It is proposed that the radiatively cooling shell may account for the variable emission pattern from objects like HH 1. Also, it is suggested that HH objects with measured space velocities that exceed the spectroscopically inferred shock velocities could correspond to heavy jets in which the bow shock is effectively adiabatic. Low-excitation objects in which these velocities are comparable may represent light jets where the jet shock is nonradiative.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Konigl, Arieh and Fryxell, Bruce A.}, year={1989}, month={Feb}, pages={L37} }
 @article{blondin_cioffi_1989, title={The growth of density perturbations in radiative shocks}, volume={345}, DOI={10.1086/167955}, abstractNote={The paper presents a new investigation of the growth of thermal instabilities behind radiative shocks. The analytic and numerical results disagree with McCray, Stein, and Kafatos, who were attempting to explain the filamentary structure commonly seen in supernova remnants, and proposed that the growth of density perturbations would lead to gross condensations in the postshock cooling region. Hydrodynamical simulations are generated which corroborate arguments in favor of no growth in the long-wavelength limit. These simulations also agree with a renewed analytic approach in the short-wavelength limit, and show that the region of rapid growth will remain inconspicuous in the overall density rise toward the back of the shock. It is noted that these calculations are in accord with some recent observations of supernova remnants where the observed filaments do not seem to have been produced by any local thermal instability process. 32 refs.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Cioffi, Denis F.}, year={1989}, month={Oct}, pages={853} }
 @article{blondin_konigl_1987, title={Pair-creation effects in accretion-shock models of active galactic nuclei}, volume={323}, DOI={10.1086/165842}, abstractNote={An exploration is undertaken of the possibility that the copious production of e(+)e(-) pairs that is expected to occur in AGNs with large compactness parameters may have an important effect on the structure of the accretion shock that may form near the central black hole in these sources. If the pairs are well coupled to the inflowing plasma, they could generate a substantial decrease in the effective value of the Eddington luminosity within the shock, and the radiation generated within the shock could play a substantial role in flow deceleration and thermalization even when the measured luminosity is far below the nominal Eddington value. The effect is demonstrated by a simple model of a planar shock that is mediated by Fermi-accelerated relativistic protons and radiation. 18 references.}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, John M. and Konigl, Arieh}, year={1987}, pages={451} }
 @article{blondin_1986, title={Hypercritical spherical accretion onto compact objects}, volume={308}, DOI={10.1086/164548}, abstractNote={On discute de modeles d'une accretion spherique, hydrodynamique, stable, a l'interieur, d'un objet compact}, journal={The Astrophysical Journal}, publisher={IOP Publishing}, author={Blondin, J. M.}, year={1986}, month={Sep}, pages={755} }
 @article{blondin_freese_1986, title={Is the 1.5-ms pulsar a young neutron star?}, volume={323}, DOI={10.1038/323786a0}, number={6091}, journal={Nature}, publisher={Springer Science and Business Media LLC}, author={Blondin, John M. and Freese, Katherine}, year={1986}, month={Oct}, pages={786–788} }