The effects of diffusion in hot subdwarf progenitors from the common envelope channel
The effects of diffusion in hot subdwarf progenitors from the common envelope channel
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DOI：
10.1093/mnras/sty158
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发表时间：
2018-02
影响因子：
4.8
通讯作者：
C. Byrne;C. Jeffery;C. Tout;Haili Hu
中科院分区：
文献类型：
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作者：
C. Byrne;C. Jeffery;C. Tout;Haili Hu
元素在大气层和恒星包层中的扩散可以极大地改变其表面成分，导致极端的化学特性。我们考虑热次矮星的情况，那里的表面氦丰度从几乎为零到几乎100%。由于热亚矮星可以通过许多不同的演化途径形成，一个关键的问题是如何将形成机制与目前的表面化学联系起来。一系列极端水平分支恒星模型是通过从红巨星中产生后普通包络星而产生的。用MESA计算了从包络弹射到堆芯氦点火的演化过程。对于有扩散和无扩散的模型，在零龄水平分支上计算了表面丰度。许多模拟还包括辐射悬浮。目标是研究从冷巨星到热亚矮星演化过程中的表面化学，并确定特征亚矮星表面何时建立。只有离开巨大的分支接近核氦点火的恒星，才会在零年龄水平分支变成富氢的亚矮星。扩散，包括辐射悬浮，在所有情况下都会耗尽初始表面氦。所有的亚矮星模型都会迅速变得比观测所允许的更加耗尽。其他元素的表面丰度总体上遵循观察到的趋势，但不是详细的。还需要额外的物理知识。
Diffusion of elements in the atmosphere and envelope of a star can drastically alter its surface composition, leading to extreme chemical peculiarities. We consider the case of hot subdwarfs, where surface helium abundances range from practically zero to almost 100 percent. Since hot subdwarfs can form via a number of different evolution channels, a key question concerns how the formation mechanism is connected to the present surface chemistry. A sequence of extreme horizontal branch star models was generated by producing post-common envelope stars from red giants. Evolution was computed with MESA from envelope ejection up to core-helium ignition. Surface abundances were calculated at the zero-age horizontal branch for models with and without diffusion. A number of simulations also included radiative levitation. The goal was to study surface chemistry during evolution from cool giant to hot subdwarf and determine when the characteristic subdwarf surface is established. Only stars leaving the giant branch close to core-helium ignition become hydrogen-rich subdwarfs at the zero-age horizontal branch. Diffusion, including radiative levitation, depletes the initial surface helium in all cases. All subdwarf models rapidly become more depleted than observations allow. Surface abundances of other elements follow observed trends in general, but not in detail. Additional physics is required.