On the Correlation between the Magnetic Activity Levels, Metallicities, and Radii of Low-Mass Stars
On the Correlation between the Magnetic Activity Levels, Metallicities, and Radii of Low-Mass Stars
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DOI：
10.1086/513142
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发表时间：
2007-01
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影响因子：
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通讯作者：
M. López-Morales
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作者：
M. López-Morales
最近，由食双星和单星干涉测量的极低质量恒星半径的数量增加，这引发了更多的问题，即是什么原因导致了观测到的半径与模型预测的半径之间的差异。提出的两个主要解释是恒星的半径与它们的活动水平或金属含量之间的关联。本文利用迄今公布的所有数据对这种相关性进行了研究。这项研究还调查了模型半径偏差与恒星质量之间的关系。样本中单星的活动水平与半径之间没有明显的相关性。这些单星是慢自转的，典型的速度是3.0公里的S。然而，在旋转较快的双星成员的情况下，存在明显的相关性。这一结果是基于恒星的X射线发射水平得出的。正如Berger等人以前指出的那样，作为金属丰度的函数，单星半径与模型的偏差似乎也有所增加。双星中的恒星似乎并不遵循同样的趋势。最后，Baraffe等人。模型很好地再现了在0.30-0.35M☉以下的半径观测，在那里恒星变得完全对流，尽管这一结果是初步的，因为在该质量范围内的几乎所有样本恒星都是慢转星，而且其中大多数的金属丰度都没有测量到。结果表明，恒星的活动性和金属丰度对确定至少在0.35M☉以上的极低质量恒星的半径起着重要作用。
The recent increase in the number of radius measurements of very low mass stars from eclipsing binaries and interferometry of single stars has raised more questions about what could be causing the discrepancy between the observed radii and those predicted by models. The two main explanations being proposed are a correlation between the radii of the stars and either their activity levels or their metallicities. This paper presents a study of such correlations using all the data published to date. The study also investigates correlations between the radius deviations from the models and the masses of the stars. There is no clear correlation between activity level and radius for the single stars in the sample. These single stars are slow rotators, with typical velocities vrot sin i < 3.0 km s-1. A clear correlation however exists in the case of the faster rotating members of binaries. This result is based on the X-ray emission levels of the stars. There also appears to be an increase in the deviation of the radii of single stars from the models as a function of metallicity, as previously indicated by Berger et al. The stars in binaries do not seem to follow the same trend. Finally, the Baraffe et al. models reproduce well the radius observations below 0.30-0.35 M☉, where the stars become fully convective, although this result is preliminary since almost all the sample stars in that mass range are slow rotators and metallicities have not been measured for most of them. The results indicate that stellar activity and metallicity play an important role in determining the radius of very low mass stars, at least above 0.35 M☉.