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arXiv 0907.3900astro-ph.SR
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热富C白矮星：通过脉动测试DB-DQ跃迁

Hot C-rich white dwarfs: testing the DB-DQ transition through pulsations

A. H. Córsico, A. D. Romero, L. G. Althaus, E. García-Berro

备注：
10 pages, 10 figures. To be published in Astronomy & Astrophysics
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摘要：

热DQ白矮星是最近在SDSS项目框架内发现的一类新的白矮星。最近，三个热DQ白矮星被报道表现出光度变化与周期兼容的脉动g-模式。在这里，我们提出了一个非绝热脉动分析最近发现的富碳热DQ白矮星星。我们的主要目标之一是通过脉动特性来测试热DQ起源的对流混合图像。我们的研究依赖于最近由Althaus等人（2009）开发的热DQ白矮星的完整演化模型，该模型始终涵盖了从再循环阶段到白矮星冷却轨道的整个演化过程。具体来说，我们提出了一个稳定性分析的白矮星模型，从阶段之前的蓝边的DBV不稳定带，直到域的热DQ白矮星，包括过渡DB -->热DQ白矮星。我们发现，在演化阶段，模型的特点是氦为主的大气，他们表现出不稳定的$g$模式脉动的DBV星的典型，当模型成为DQ白矮星与碳为主的大气，他们继续脉动不稳定的特性类似于DB模型，并在协议中检测到的周期可变热DQ白矮星。我们的计算提供了强有力的支持对流混合图片热DQ的形成。特别是，我们的研究结果指出存在脉动DB白矮星非常薄的氦丰富的信封，通过DBV不稳定带后，成为可变热DQ星。这些具有非常薄的包层的DB星的存在可以通过星震学来研究。

英文摘要：

Hot DQ white dwarfs constitute a new class of white dwarf stars, uncovered recently within the framework of the SDSS project. Recently, three hot DQ white dwarfs have been reported to exhibit photometric variability with periods compatible with pulsation g-modes. Here, we present a nonadiabatic pulsation analysis of the recently discovered carbon-rich hot DQ white dwarf stars. One of our main aims is to test the convective-mixing picture for the origin of hot DQs through the pulsational properties. Our study relies on the full evolutionary models of hot DQ white dwarfs recently developed by Althaus et al. (2009), that consistently cover the whole evolution from the born-again stage to the white dwarf cooling track. Specifically, we present a stability analysis of white dwarf models from stages before the blue edge of the DBV instability strip until the domain of the hot DQ white dwarfs, including the transition DB --> hot DQ white dwarf. We found that at evolutionary phases in which the models are characterized by He-dominated atmospheres, they exhibit unstable $g$-mode pulsations typical of DBV stars, and when the models become DQ white dwarfs with carbon-dominated atmospheres, they continue being pulsationally unstable with similar characteristics than DB models, and in agreement with the periods detected in variable hot DQ white dwarfs. Our calculations provide strong support to the convective-mixing picture for the formation of hot DQs. In particular, our results point to the existence of pulsating DB white dwarfs with very thin He-rich envelopes, which after passing the DBV instability strip become variable hot DQ stars. The existence of these DB stars with very thin envelopes could be investigated through asteroseismology.

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