CHROMOSPHERIC VARIABILITY IN SLOAN DIGITAL SKY SURVEY M DWARFS. II. SHORT-TIMESCALE Hα VARIABILITY
CHROMOSPHERIC VARIABILITY IN SLOAN DIGITAL SKY SURVEY M DWARFS. II. SHORT-TIMESCALE Hα VARIABILITY
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DOI：
10.1088/0004-637x/722/2/1352
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发表时间：
2009-11
期刊：
影响因子：
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通讯作者：
Ethan Kruse;E. Berger;G. Knapp;T. Laskar;J. Gunn;C. Loomis;R. Lupton;D. Schlegel
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作者：
Ethan Kruse;E. Berger;G. Knapp;T. Laskar;J. Gunn;C. Loomis;R. Lupton;D. Schlegel
我们利用斯隆数字巡天中52392个天体的单次15分钟光谱曝光数据，首次对M型矮星的短时标色球层Hα变异性进行了全面研究。我们的样本在M0 - M9范围内每个光谱型区间包含约10³ - 10⁴个天体，每个天体通常有三次曝光（最多可达30次曝光）。利用这个庞大的数据集，我们发现约16%的源在至少一次曝光中呈现Hα发射，其中约45%在所有可用曝光中都呈现Hα发射。与之前对Hα活动（LHα/Lbol）的研究一样，我们发现从M0 - M6，活动天体的比例迅速增加。然而，我们发现在更晚的光谱型中该比例随后下降，我们将其归因于我们使用了单独的光谱。同样，我们发现对于光谱型M0 - M5，活动在LHα/Lbol≈10⁻³.⁶的水平达到饱和，随后在M7 - M9范围内下降到约10⁻⁴.³。在有Hα发射的天体样本中，只有26%与无变化发射相符，且与光谱型无关。Hα变异性通过最大与最小Hα等效宽度之比（REW）来量化，从M0到M5呈现快速上升，随后在M9天体中出现平台期并可能下降。特别是，REW≳10的变异性仅在M5之后的天体中观测到，生存分析表明M0 - M4和M5 - M9的REW值来自同一分布的概率≲0.1%。我们还发现，对于指数分布，对于M0 - M4，REW值遵循N(REW)∝exp[ − (REW − 1)/2.3]，对于M5 - M9遵循∝exp[ − (REW − 1)/2.9]。最后，比较具有持续和间歇Hα发射的天体，我们发现后者呈现出更大的变异性。基于这些结果，我们得出结论：在15分钟到1小时的时间尺度上，M型矮星的Hα变异性随着光谱型变晚而增加，并且间歇源的变异性更大。
We present the first comprehensive study of short-timescale chromospheric Hα variability in M dwarfs using the individual 15 minute spectroscopic exposures for 52, 392 objects from the Sloan Digital Sky Survey. Our sample contains about 103–104 objects per spectral type bin in the range M0–M9, with a typical number of three exposures per object (ranging up to a maximum of 30 exposures). Using this extensive data set, we find that about 16% of the sources exhibit Hα emission in at least one exposure, and of those about 45% exhibit Hα emission in all of the available exposures. As in previous studies of Hα activity (LHα/Lbol), we find a rapid increase in the fraction of active objects from M0–M6. However, we find a subsequent decline in later spectral types that we attribute to our use of the individual spectra. Similarly, we find saturated activity at a level of LHα/Lbol ≈ 10−3.6 for spectral types M0–M5 followed by a decline to about 10−4.3 in the range M7–M9. Within the sample of objects with Hα emission, only 26% are consistent with non-variable emission, independent of spectral type. The Hα variability, quantified in terms of the ratio of maximum to minimum Hα equivalent width (REW), exhibits a rapid rise from M0 to M5, followed by a plateau and a possible decline in M9 objects. In particular, variability with REW ≳ 10 is only observed in objects later than M5, and survival analysis indicates a probability of ≲0.1% that the REW values for M0–M4 and M5–M9 are drawn from the same distribution. We further find that for an exponential distribution, the REW values follow N(REW) ∝ exp[ − (REW − 1)/2.3] for M0–M4 and ∝exp[ − (REW − 1)/2.9] for M5–M9. Finally, comparing objects with persistent and intermittent Hα emission, we find that the latter exhibit greater variability. Based on these results, we conclude that Hα variability in M dwarfs on timescales of 15 minutes to 1 hr increases with later spectral type, and that the variability is larger for intermittent sources.