Atmospheric parameters and carbon abundance for hot DB white dwarfs
Atmospheric parameters and carbon abundance for hot DB white dwarfs
复制标题
热 DB 白矮星的大气参数和碳丰度
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
B. Gansicke
中科院分区：
文献类型：
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作者：
D. Koester;J. Provencal;B. Gansicke
热DB（氦气氛）白色矮星在有效温度25000 K附近的大气参数是非常难以确定的光谱。这是特别不幸的，因为这是可变的DBV或V777 Her恒星的范围。需要有准确的大气参数来帮助或确认对这些物体的星震分析。另一个重要的方面是Dufour等人（2007）发现的一类新的白色矮星--热DQ，其光谱以碳线为主。分析表明它们的大气是纯碳。这些恒星的起源还不清楚，但它们可能与这里研究的更热的DBs有进化联系。我们的目标是确定准确的大气参数和元素丰度，并研究光谱类DB和热DQ的白色矮星演化的影响。利用模式大气研究了五种DBs的高分辨紫外光谱。我们确定恒星的参数和丰度或上限的C和Si。这些对象相比，低于20000 K的冷却器DB。我们发现光球的C和没有其他重元素-与C/Si比极高的限制-在两个五个热DBs。我们比较了文献中提出的对这种不寻常组成的各种解释：星际或星周物质的吸积、辐射悬浮、从氦层以下更深的内部挖掘出的碳以及残余恒星风。这些解释都不是完全令人满意的，热DQ的起源问题仍然是一个悬而未决的问题。
Atmospheric parameters for hot DB (helium atmosphere) white dwarfs near effective temperatures of 25000K are extremely difficult to determine from optical spectroscopy. This is particularly unfortunate, because this is the range of variable DBV or V777 Her stars. Accurate atmospheric parameters are needed to help or confirm the asteroseismic analysis of these objects. Another important aspect is the new class of white dwarfs - the hot DQ - detected by Dufour et al. (2007), with spectra dominated by carbon lines. The analysis shows that their atmospheres are pure carbon. The origin of these stars is not yet understood, but they may have an evolutionary link with the hotter DBs as studied here. Our aim is to determine accurate atmospheric parameters and element abundances and study the implications for the evolution white dwarfs of spectral classes DB and hot DQ. High resolution UV spectra of five DBs are studied with model atmospheres. We determine stellar parameters and abundances or upper limits of C and Si. These objects are compared with cooler DBs below 20000K. We find photospheric C and no other heavy elements - with extremely high limits on the C/Si ratio - in two of the five hot DBs. We compare various explanations for this unusual composition, which have been proposed in the literature: accretion of interstellar or circumstellar matter, radiative levitation, carbon dredge-up from deeper interior below the helium layer, and a residual stellar wind. None of these explanations is completely satisfactory, and the problem of the origin of the hot DQ remains an open question.