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Article overview
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Subdwarf B stars from the common envelope ejection channel | H. Xiong
; X. Chen
; P. Podsiadlowski
; Z. Han
; | Date: |
1 Sep 2016 | Abstract: | From the canonical binary scenario, the majority of sdBs are produced from
low-mass stars with degenerate cores where helium is ignited in a way of
flashes. Due to numerical difficulties, the models of produced sdBs are
generally constructed from more massive stars with non-degenerate cores,
leaving several uncertainties on the exact characteristics of sdB stars.
Employing MESA, we systematically studied the characteristics of sdBs produced
from the common envelope (CE) ejection channel, and found that the sdB stars
produced from the CE ejection channel appear to form two distinct groups on the
effective temperature-gravity diagram. One group (the flash-mixing model)
almost has no H-rich envelope and crows at the hottest temperature end of the
extremely horizontal branch (EHB), while the other group has significant H-rich
envelope and spreads over the whole canonical EHB region. The key factor for
the dichotomy of the sdB properties is the development of convection during the
first helium flash, which is determined by the interior structure of the star
after the CE ejection. For a given initial stellar mass and a given core mass
at the onset of the CE, if the CE ejection stops early, the star has a
relatively massive H-rich envelope, resulting in a canonical sdB generally. The
fact of only a few short-orbital-period sdB binaries being in the flash-mixing
sdB region and the lack of He-rich sdBs in short-orbital-period binaries
indicate that the flash mixing is not very often in the products of the CE
ejection. A falling back process after the CE ejection, similar to that
happened in nova, is an appropriate way of increasing the envelope mass, then
prevents the flash mixing. | Source: | arXiv, 1608.8739 | Services: | Forum | Review | PDF | Favorites |
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