论文标题
对流挖掘模型作为DBA白色矮人中氢的起源
A Convective Dredge-Up Model as the Origin of Hydrogen in DBA White Dwarfs
论文作者
论文摘要
我们使用一组新的包络模型计算与分层和混合的氢/氦组成的新型包膜模型计算，我们重新审视了DB白色矮人形成的问题以及DBA恒星中氢的起源。我们首先描述了一个近似模型，以模拟所谓的对流稀释过程，其中薄而浅表的氢辐射层逐渐被下面的和更大的对流氦络构造逐渐侵蚀，从而将Da White Dwarf转化为DB恒星。我们表明，这种对流稀释过程能够说明DB白色矮人低于Teff 〜20,000 K的数量的大幅增加，但是此过程预期的残留氢丰度仍然比DBA白矮人中观察到的数量级低。经常调用涉及星际培养基或其他外体的氢积聚的方案，以解释这些过度的氢气。在本文中，我们描述了一种新的范式，其中最初在厚恒星包膜内稀释的氢仍然存在，并在Teff 〜20,000 K白矮人的深层中缓慢地向上扩散。当对流稀释过程发生时，混合H/HE对流区的底部沉入了恒星深处，导致大量氢被挖出到恒星表面，这种现象类似于DQ White Dwarfs中所调用的现象。
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 diffusing 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.
