Spectroscopic Properties of Cool Stars in the Sloan Digital Sky Survey: An Analysis of Magnetic Activity and a Search for Subdwarfs
Spectroscopic Properties of Cool Stars in the Sloan Digital Sky Survey: An Analysis of Magnetic Activity and a Search for Subdwarfs
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DOI：
10.1086/421364
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发表时间：
2004-03
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通讯作者：
A. West;S. Hawley;L. Walkowicz;K. Covey;N. Silvestri;S. Raymond;H. Harris;J. Munn;P. McGehee;P. McGehee;Ž. Ivezić;Ž. Ivezić;J. Brinkmann
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作者：
A. West;S. Hawley;L. Walkowicz;K. Covey;N. Silvestri;S. Raymond;H. Harris;J. Munn;P. McGehee;P. McGehee;Ž. Ivezić;Ž. Ivezić;J. Brinkmann
我们对斯隆数字巡天中近8000颗晚型矮星进行了光谱分析。利用Hα发射线作为活动指标，我们研究了活动恒星的比例随光谱型的变化，发现在M8型附近有一个峰值，这证实了先前的结果。与以往的发现不同，我们发现并非所有M7 - M8型恒星都是活动的。我们表明这可能是先前样本距离分布的一种选择效应，因为活动恒星似乎集中在银道面附近。我们还检查了每颗恒星的活动强度（Hα发射光度与全辐射光度之比），发现平均活动强度在M0 - M5范围内是恒定的，在更晚的类型中下降。这种下降开始的光谱型比先前发现的略早。我们探究了活动对宽波段测光颜色的影响，发现活动恒星和非活动恒星之间没有显著差异。我们还使用光谱金属丰度指标寻找了亚矮星，发现了60个亚矮星候选体。其中几个候选体接近极端亚矮星边界。与具有相同r - i颜色的盘矮星相比，光谱亚矮星候选体在g - r波段红约0.2星等。
We present a spectroscopic analysis of nearly 8000 late-type dwarfs in the Sloan Digital Sky Survey. Using the Hα emission line as an activity indicator, we investigate the fraction of active stars as a function of spectral type and find a peak near type M8, confirming previous results. In contrast to past findings, we find that not all M7–M8 stars are active. We show that this may be a selection effect of the distance distributions of previous samples, since the active stars appear to be concentrated near the Galactic plane. We also examine the activity strength (ratio of the luminosity emitted in Hα to the bolometric luminosity) for each star and find that the mean activity strength is constant over the range M0–M5 and declines at later types. The decline begins at a slightly earlier spectral type than previously found. We explore the effect that activity has on the broadband photometric colors and find no significant differences between active and inactive stars. We also carry out a search for subdwarfs using spectroscopic metallicity indicators and find 60 subdwarf candidates. Several of these candidates are near the extreme subdwarf boundary. The spectroscopic subdwarf candidates are redder by ∼0.2 mag in g-r compared with disk dwarfs at the same r-i color.