Query : 2008A&A...491..253M

2008A&A...491..253M - Astronomy and Astrophysics, volume 491, 253-265 (2008/11-3)

Modeling He-rich subdwarfs through the hot-flasher scenario.


Abstract (from CDS):

We present 1D numerical simulations aimed at studying the hot-flasher scenario for the formation of He-rich subdwarf stars. Sequences were calculated for a wide range of metallicities and physical assumptions, such as the stellar mass at the moment of the helium core flash. This allows us to study the two previously proposed flavors of the hot-flasher scenario (``deep'' and ``shallow'' mixing cases) and to identify a third transition type. Our sequences are calculated by solving simultaneously the mixing and burning equations within a diffusive convection picture, and in the context of standard mixing length theory. We are able to follow chemical evolution during deep-mixing events in which hydrogen is burned violently, and therefore able to present a homogeneous set of abundances for different metallicities and varieties of hot-flashers. We extend the scope of our work by analyzing the effects of non-standard assumptions, such as the effect of chemical gradients, extra-mixing at convective boundaries, possible reduction in convective velocities, or the interplay between difussion and mass loss. Particular emphasis is placed on the predicted surface properties of the models. We find that the hot-flasher scenario is a viable explanation for the formation and surface properties of He-sdO stars. Our results also show that, during the early He-core burning stage, element diffusion may produce the transformation of (post hot-flasher) He-rich atmospheres into He-deficient ones. If this is so, then we find that He-sdO stars should be the progenitors of some of the hottest sdB stars.

Abstract Copyright:

Journal keyword(s): stars: evolution - stars: horizontal-branch - stars: subdwarfs - stars: mass-loss

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 LB 1766 HS* 04 59 18.7820628456 -53 52 54.594838668 10.88 12.25 12.91     sdBHe 18 0
2 NGC 2808 GlC 09 12 03.10 -64 51 48.6           ~ 1424 0
3 NGC 5139 GlC 13 26 47.28 -47 28 46.1           ~ 3433 0
4 PG 1544+488 HS* 15 46 11.6930203944 +48 38 37.228874928   12.52 12.79 13.08   sdBC1VIIpHe39 50 1

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