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arXiv 1708.00482astro-ph.SR
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新演化序列框架中的脉动低质量白矮星:V. ELMV白矮星星的星震学

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences: V. Asteroseismology of ELMV white dwarf stars

Leila M. Calcaferro, Alejandro H. Córsico, Leandro G. Althaus

摘要:

在过去的几年里,在我们的银河系中发现了许多脉动的低质量白矮星。鉴于其中一些行星表现出亮度的多周期变化,因此有可能通过星震学来探测它们的内部。我们提出了一个详细的小质量变星白矮星星的星震学研究的基础上,一套完整的低质量氦核白矮星星代表的完全演化模型。我们采用绝热径向和非径向脉动周期的低质量白矮星模型的恒星质量范围从$0.1554$到$0.4352\ M_{\odot}$,这是通过模拟一个二元系统的非保守演化的初始$1 M_{\odot}$ ZAMS星和$1.4 M_{\odot}$中子星的伴侣。我们估计了所研究恒星的平均周期间隔,然后将观测到的周期间隔与计算出的周期间隔的平均值进行比较,用于我们的模型网格,以限制恒星质量。我们还利用每个已知脉动低质量白矮星的单个观测周期来寻找具有代表性的地震学模型。我们发现,即使分析下的恒星表现出几个周期和周期拟合显示的解决方案的多样性,它是可能的,找到地震模型的质量和有效温度是在协议的光谱给出的值,在大多数情况下。在两种情况下,我们可以从观测到的周期集合中提取周期间隔,这种方法导致恒星质量的值大大大于这类恒星的预期值。这项工作中提出的结果表明,一方面需要进一步进行光度测定研究,另一方面需要对理论模型进行某些改进,以便将小行星地震学结果置于更坚实的基础之上。

英文摘要:

Many pulsating low-mass white-dwarf stars have been detected in the last years in the field of our Galaxy. Given that some of them exhibit multiperiodic variation of brightness, it is possible to probe their interiors through asteroseismology. We present a detailed asteroseismological study of all the known low-mass variable white dwarf stars based on a complete set of fully evolutionary models representative of low-mass He-core white dwarf stars. We employed adiabatic radial and nonradial pulsation periods for low-mass white dwarf models with stellar masses ranging from $0.1554$ to $0.4352\ M_{\odot}$, that were derived by simulating the nonconservative evolution of a binary system consisting of an initially $1 M_{\odot}$ ZAMS star and a $1.4 M_{\odot}$ neutron star companion. We estimated the mean period spacing for the stars under study and then we used the comparison between the observed period spacing with the average of the computed period spacings for our grid of models to constrain the stellar mass. We also employed the individual observed periods of every known pulsating low-mass white dwarf star, to search for a representative seismological model. We found that even though the stars under analysis exhibit few periods and the period fits show multiplicity of solutions, it is possible to find seismological models whose mass and effective temperature are in agreement with the values given by spectroscopy, for most of the cases. In the two cases where we could extract the period spacing from the set of observed periods, this method led to values of the stellar masses substantially larger than expected for this type of stars. The results presented in this work show in the one hand, the need for further photometric searches, and on the other hand, some improvements of the theoretical models, in order to place the asteroseismological results on a firmer ground.

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