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arXiv 0908.4092astro-ph.SRastro-ph.EP
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M-矮星的自转速度

Rotation Velocities for M-dwarfs

J S Jenkins, L W Ramsey, H R A Jones, Y Pavlenko, J Gallardo, J R Barnes, D J Pinfield

备注：
22 pages, 11 figures, 4 tables, Accepted for publication in ApJ
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摘要：

我们目前的光谱旋转速度（v sin i）的56 M矮星使用高分辨率的HET HRS红色光谱。此外，我们还确定了光度有效温度，质量和金属丰度（[Fe/H]）的一些恒星观察到这里和文献中，我们可以获得准确的视差测量和相关的测光。我们已经增加了约80%的中M恒星的已知v sin的数量，可以确认一个弱的旋转速度随着有效温度的降低而增加。我们的vsin样本在低速（~3 km/s）时达到峰值。我们发现早期M和晚期M星之间的旋转速度分布的变化，这可能是由于部分和完全对流星之间的场拓扑结构的变化。也有可能进一步的变化，在旋转分布向晚M矮星的地方，尘埃开始发挥作用的恒星大气。我们还将v sin i与年龄联系起来，并展示了如何使用它来提供中M恒星的年龄限制。当把所有文献中M矮星的速度加到我们的样本中时，有198个v sin i小于或等于10 km/s，124个在M星的中后期（M3.0-M9.5），在那里测量精确的光学径向速度是困难的。此外，我们还搜索任何显着的H α发射或吸收的光谱。发现43%的天体具有这种辐射，可能代表年轻的活跃天体，具有高水平的径向速度噪声。这里给出的表格将有助于任何未来的M星行星搜索目标的选择，以提取恒星，将表现出低径向速度抖动。

英文摘要：

We present spectroscopic rotation velocities (v sin i) for 56 M dwarf stars using high resolution HET HRS red spectroscopy. In addition we have also determined photometric effective temperatures, masses and metallicities ([Fe/H]) for some stars observed here and in the literature where we could acquire accurate parallax measurements and relevant photometry. We have increased the number of known v sin is for mid M stars by around 80% and can confirm a weakly increasing rotation velocity with decreasing effective temperature. Our sample of v sin is peak at low velocities (~3 km/s). We find a change in the rotational velocity distribution between early M and late M stars, which is likely due to the changing field topology between partially and fully convective stars. There is also a possible further change in the rotational distribution towards the late M dwarfs where dust begins to play a role in the stellar atmospheres. We also link v sin i to age and show how it can be used to provide mid-M star age limits. When all literature velocities for M dwarfs are added to our sample there are 198 with v sin i less than or equal to 10 km/s and 124 in the mid-to-late M star regime (M3.0-M9.5) where measuring precision optical radial-velocities is difficult. In addition we also search the spectra for any significant Halpha emission or absorption. 43% were found to exhibit such emission and could represent young, active objects with high levels of radial-velocity noise. The tables presented here will aid any future M star planet search target selection to extract stars that will exhibit low radial-velocity jitter.

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