A Convective Dredge-up Model as the Origin of Hydrogen in DBA White Dwarfs
A Convective Dredge-up Model as the Origin of Hydrogen in DBA White Dwarfs
复制标题
DBA白矮星氢起源的对流挖掘模型
DOI：
10.3847/1538-4357/ab6602
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
G. Fontaine
中科院分区：
文献类型：
--
作者：
B. Rolland;P. Bergeron;G. Fontaine
我们重新审视了DB白矮星的形成问题，以及DBA恒星中氢的起源，使用了一套新的包络模型计算，具有分层和混合的氢/氦组成。我们首先描述了一个近似模型来模拟所谓的对流稀释过程，在这个过程中，一个薄的、表面的氢辐射层逐渐被底层更大质量的对流氦包层侵蚀，从而将DA白矮星转变为DB星。我们表明，这种对流稀释过程能够解释Teff ~ 20,000 K以下DB白矮星数量的大量增加，但从这一过程中预期的剩余氢丰度仍然比DBA白矮星中观察到的低几个数量级。从星际介质或其他外部天体吸积氢的情况经常被用来解释这些过量的氢。在这篇论文中，我们描述了一种新的范式，在这种范式中，氢最初在厚厚的恒星包层中被稀释，但仍然存在，并在Teff ~ 20,000 K白矮星的更深层中缓慢向上扩散。当对流稀释过程发生时，混合H/He对流区的底部下沉到恒星深处，导致大量的氢被吸到恒星表面，这一现象与DQ白矮星的情况类似。
We revisit the problem of the formation of DB white dwarfs, as well as the origin of hydrogen in DBA stars, using a new set of envelope model calculations with stratified and mixed hydrogen/helium compositions. We first describe an approximate model to simulate the so-called convective dilution process, where a thin, superficial hydrogen radiative layer is gradually eroded by the underlying and more massive convective helium envelope, thus transforming a DA white dwarf into a DB star. We show that this convective dilution process is able to account for the large increase in the number of DB white dwarfs below Teff ∼ 20,000 K, but that the residual hydrogen abundances expected from this process are still orders of magnitude lower than those observed in DBA white dwarfs. Scenarios involving the accretion of hydrogen from the interstellar medium or other external bodies have often been invoked to explain these overabundances of hydrogen. In this paper, we describe a new paradigm where hydrogen, initially diluted within the thick stellar envelope, is still present and slowly diffuses upward in the deeper layers of a Teff ∼ 20,000 K white dwarf. When the convective dilution process occurs, the bottom of the mixed H/He convection zone sinks deep into the star, resulting in large amounts of hydrogen being dredged up to the stellar surface, a phenomenon similar to that invoked in the context of DQ white dwarfs.
影响因子：
3.5
作者：
K. Werner;F. Herwig
通讯作者：
K. Werner;F. Herwig