| 1. |
- Dan, M., et al.
(författare)
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Thermonuclear detonations ensuing white dwarf mergers
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 454:4, s. 4411-4428
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Tidskriftsartikel (refereegranskat)abstract
- The merger of two white dwarfs (WDs) has for many years not been considered as the favoured model for the progenitor system of Type Ia supernovae (SNe Ia). But recent years have seen a change of opinion as a number of studies, both observational and theoretical, have concluded that they should contribute significantly to the observed SN Ia rate. In this paper, we study the ignition and propagation of detonation through post-merger remnants and we follow the resulting nucleosynthesis up to the point where a homologous expansion is reached. In our study we cover the entire range of WD masses and compositions. For the emergence of a detonation we study three different setups. The first two are guided by the merger remnants from our earlier simulations, while for the third one the ignitions were set by placing hotspots with properties determined by spatially resolved calculations taken from the literature. There are some caveats to our approach which we investigate. We carefully compare the nucleosynthetic yields of successful explosions with SN Ia observations. Only three of our models are consistent with all the imposed constraints and potentially lead to a standard Type Ia event. The first one, a 0.45 M-circle dot helium (He) + 0.9 M-circle dot carbon-oxygen (CO) WD system produces a sub-luminous, SN 1991bg-like event while the other two, a 0.45M(circle dot) He+1.1 M-circle dot oxygen-neon WD system and a 1.05 + 1.05 M-circle dot system with two CO WDs, are good candidates for common SNe Ia.
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| 2. |
- Gafton, Emanuel, et al.
(författare)
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Relativistic effects on tidal disruption kicks of solitary stars
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 449:1, s. 771-780
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Tidskriftsartikel (refereegranskat)abstract
- Solitary stars that wander too close to their galactic centres can become tidally disrupted, if the tidal forces due to the supermassive black hole residing there overcome the self-gravity of the star. If the star is only partially disrupted, so that a fraction survives as a self-bound object, this remaining core will experience a net gain in specific orbital energy, which translates into a velocity 'kick' of up to similar to 10(3) km s(-1). In this paper, we present the result of smoothed particle hydrodynamics simulations of such partial disruptions, and analyse the velocity kick imparted on the surviving core. We compare gamma = 5/3 and gamma = 4/3 polytropes disrupted in both a Newtonian potential, and a generalized potential that reproduces most relativistic effects around a Schwarzschild black hole either exactly or to excellent precision. For the Newtonian case, we confirm the results of previous studies that the kick velocity of the surviving core is virtually independent of the ratio of the black hole to stellar mass, and is a function of the impact parameter beta alone, reaching at most the escape velocity of the original star. For a given beta, relativistic effects become increasingly important for larger black holemasses. In particular, we find that the kick velocity increases with the black hole mass, making larger kicks more common than in the Newtonian case, as low-beta encounters are statistically more likely than high-beta encounters. The analysis of the tidal tensor for the generalized potential shows that our results are robust lower limits on the true relativistic kick velocities, and are generally in very good agreement with the exact results.
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