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178 Publications visible to you, out of a total of 178
Fully compressible simulations of waves and core convection in main-sequence stars

Abstract (Expand)

Context. Recent, nonlinear simulations of wave generation and propagation in full-star models have been carried out in the anelastic approximation using spectral methods. Although it makes long time … steps possible, this approach excludes the physics of sound waves completely and requires rather high artificial viscosity and thermal diffusivity for numerical stability. A direct comparison with observations is thus limited. Aims. We explore the capabilities of our compressible multidimensional Seven-League Hydro (SLH) code to simulate stellar oscillations. Methods. We compare some fundamental properties of internal gravity and pressure waves in 2D SLH simulations to linear wave theory using two test cases: (1) an interval gravity wave packet in the Boussinesq limit and (2) a realistic 3 M⊙ stellar model with a convective core and a radiative envelope. Oscillation properties of the stellar model are also discussed in the context of observations. Results. Our tests show that specialized low-Mach techniques are necessary when simulating oscillations in stellar interiors. Basic properties of internal gravity and pressure waves in our simulations are in good agreement with linear wave theory. As compared to anelastic simulations of the same stellar model, we can follow internal gravity waves of much lower frequencies. The temporal frequency spectra of velocity and temperature are flat and compatible with the observed spectra of massive stars. Conclusion. The low-Mach compressible approach to hydrodynamical simulations of stellar oscillations is promising. Our simulations are less dissipative and require less luminosity boosting than comparable spectral simulations. The fully-compressible approach allows for the coupling of gravity and pressure waves in the outer convective envelopes of evolved stars to be studied in the future.

Authors: L. Horst, P. V. F. Edelmann, R. Andrássy, F. K. Röpke, D. M. Bowman, C. Aerts, R. P. Ratnasingam

Date Published: 1st Sep 2020

Publication Type: Journal

Photometric detection of internal gravity waves in upper main-sequence stars

Abstract (Expand)

Context. Massive stars are predicted to excite internal gravity waves (IGWs) by turbulent core convection and from turbulent pressure fluctuations in their near-surface layers. These IGWs are extremely … efficient at transporting angular momentum and chemical species within stellar interiors, but they remain largely unconstrained observationally. Aims. We aim to characterise the photometric detection of IGWs across a large number of O and early-B stars in the Hertzsprung–Russell diagram, and explain the ubiquitous detection of stochastic variability in the photospheres of massive stars. Methods. We combined high-precision time-series photometry from the NASA Transiting Exoplanet Survey Satellite with high-resolution ground-based spectroscopy of 70 stars with spectral types O and B to probe the relationship between the photometric signatures of IGWs and parameters such as spectroscopic mass, luminosity, and macroturbulence. Results. A relationship is found between the location of a star in the spectroscopic Hertzsprung–Russell diagram and the amplitudes and frequencies of stochastic photometric variability in the light curves of massive stars. Furthermore, the properties of the stochastic variability are statistically correlated with macroturbulent velocity broadening in the spectral lines of massive stars. Conclusions. The common ensemble morphology for the stochastic low-frequency variability detected in space photometry and its relationship to macroturbulence is strong evidence for IGWs in massive stars, since these types of waves are unique in providing the dominant tangential velocity field required to explain the observed spectroscopy.

Authors: D. M. Bowman, S. Burssens, S. Simón-Díaz, P. V. F. Edelmann, T. M. Rogers, L. Horst, F. K. Röpke, C. Aerts

Date Published: 1st Aug 2020

Publication Type: Journal

Polluting the Pair-instability Mass Gap for Binary Black Holes through Super-Eddington Accretion in Isolated Binaries

Abstract (Expand)

The theory for single stellar evolution predicts a gap in the mass distribution of black holes (BHs) between approximately 45 and 130 $\,{M}_{\odot }$, the so-called "pair-instability mass gap." … We examine whether BHs can pollute the gap after accreting from a stellar companion. To this end, we simulate the evolution of isolated binaries using a population synthesis code, where we allow for super-Eddington accretion. Under our most extreme assumptions, we find that at most about 2% of all merging binary BH systems contains a BH with a mass in the pair-instability mass gap, and we find that less than 0.5% of the merging systems has a total mass larger than 90 $\,{M}_{\odot }$. We find no merging binary BH systems with a total mass exceeding 100 $\,{M}_{\odot }$. We compare our results to predictions from several dynamical pathways to pair-instability mass gap events and discuss the distinguishable features. We conclude that the classical isolated binary formation scenario will not significantly contribute to the pollution of the pair-instability mass gap. The robustness of the predicted mass gap for the isolated binary channel is promising for the prospective of placing constraints on (i) the relative contribution of different formation channels, (ii) the physics of the progenitors including nuclear reaction rates, and, tentatively, (iii) the Hubble parameter.

Authors: L. A. C. van Son, S. E. De Mink, F. S. Broekgaarden, M. Renzo, S. Justham, E. Laplace, J. Morán-Fraile, D. D. Hendriks, R. Farmer

Date Published: 1st Jul 2020

Publication Type: Journal

The Spectacular Ultraviolet Flash from the Peculiar Type Ia Supernova 2019yvq

Abstract

Not specified

Authors: A. A. Miller, M. R. Magee, A. Polin, K. Maguire, E. Zimmerman, Y. Yao, J. Sollerman, S. Schulze, D. A. Perley, M. Kromer, S. Dhawan, M. Bulla, I. Andreoni, E. C. Bellm, K. De, R. Dekany, A. Delacroix, C. Fremling, A. Gal-Yam, D. A. Goldstein, V. Z. Golkhou, A. Goobar, M. J. Graham, I. Irani, M. M. Kasliwal, S. Kaye, Y. -L. Kim, R. R. Laher, A. A. Mahabal, F. J. Masci, P. E. Nugent, E. Ofek, E. S. Phinney, S. J. Prentice, R. Riddle, M. Rigault, B. Rusholme, T. Schweyer, D. L. Shupe, M. T. Soumagnac, G. Terreran, R. Walters, L. Yan, J. Zolkower, S. R. Kulkarni

Date Published: 1st Jul 2020

Publication Type: Journal

SNe Ia from double detonations: Impact of core-shell mixing on the carbon ignition mechanism

Abstract (Expand)

Sub-Chandrasekhar mass white dwarfs accreting a helium shell on a carbon-oxygen core are potential progenitors of normal Type Ia supernovae. This work focuses on the details of the onset of the carbon … detonation in the double detonation sub-Chandrasekhar model. In order to simulate the influence of core-shell mixing on the carbon ignition mechanism, the helium shell and its detonation are followed with an increased resolution compared to the rest of the star treating the propagation of the detonation wave more accurately. This significantly improves the predictions of the nucleosynthetic yields from the helium burning. The simulations were carried out with the AREPO code. A carbon-oxygen core with a helium shell was set up in one dimension and mapped to three dimensions. We ensured the stability of the white dwarf with a relaxation step before the hydrodynamic detonation simulation started. Synthetic observables were calculated with the radiative transfer code ARTIS. An ignition mechanism of the carbon detonation was observed, which received little attention before. In this "scissors mechanism", the impact the helium detonation wave has on unburnt material when converging opposite to its ignition spot is strong enough to ignite a carbon detonation. This is possible in a carbon enriched transition region between the core and shell. The detonation mechanism is found to be sensitive to details of the core-shell transition and our models illustrate the need to consider core-shell mixing taking place during the accretion process. Even though the detonation ignition mechanism differs form the converging shock mechanism, the differences in the synthetic observables are not significant. Though they do not fit observations better than previous simulations, they illustrate the need for multi-dimensional simulations.

Authors: Sabrina Gronow, Christine Collins, Sebastian T. Ohlmann, Rüdiger Pakmor, Markus Kromer, Ivo R. Seitenzahl, Stuart A. Sim, Friedrich K. Röpke

Date Published: 1st Mar 2020

Publication Type: Journal

White dwarf deflagrations for Type Iax supernovae: polarisation signatures from the explosion and companion interaction

Abstract

Not specified

Authors: M. Bulla, Z. -W. Liu, F. K. Röpke, S. A. Sim, M. Fink, M. Kromer, R. Pakmor, I. R. Seitenzahl

Date Published: 1st Mar 2020

Publication Type: Journal

Monte Carlo radiative transfer for the nebular phase of Type Ia supernovae

Abstract

Not specified

Authors: L. J. Shingles, S. A. Sim, M. Kromer, K. Maguire, M. Bulla, C. Collins, C. P. Ballance, A. S. Michel, C. A. Ramsbottom, F. K. Röpke, I. R. Seitenzahl, N. B. Tyndall

Date Published: 1st Feb 2020

Publication Type: Journal

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