Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars
Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars
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DOI：
10.1051/0004-6361/201833498
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发表时间：
2018-07
影响因子：
6.5
通讯作者：
M. Mittag;J. Schmitt;K.-P. Schroder Hamburger Sternwarte;U. Hamburg;D. O. Astronomy;U. Guanajuato
中科院分区：
文献类型：
--
作者：
M. Mittag;J. Schmitt;K.-P. Schroder Hamburger Sternwarte;U. Hamburg;D. O. Astronomy;U. Guanajuato
恒星自转，恒星活动和对流周转时间之间的连接被重新审视，重点是磁活动的唯一贡献的钙II H&K排放，所谓的过剩通量，其无量纲指标R+HK与其他恒星参数和活动指标。我们的研究是基于169个主序星的样本，直接测量威尔逊山的S指数和旋转周期。R+HK值是从相应的S指数导出的，并且与各种B-V颜色间隔中的旋转周期有关。首先，我们表明，恒星的磁性活动消失，即恒星的过剩通量指数R+HK接近零，有一个明确的，颜色依赖的旋转周期分布，我们还表明，这种旋转周期分布适用于大样本的冷星的旋转周期最近变得可用。其次，我们使用的经验参数，以等同于全球对流周转时间，这是一种方法，使我们能够获得明确的磁活动相关的过剩通量指数R+HK，旋转周期和Rossby数之间的关系。第三，我们表明，活动与Rossby数的关系是非常相似的，在不同的活动指标。由于我们的研究，我们强调，我们的Rossby数的基础上的全球对流周转时间的方法，但不超过统一，即使是完全不活跃的恒星。此外，一旦使用适当的比例，轮调-活动关系可能对不同的活动指标具有普遍性。
The connection between stellar rotation, stellar activity, and convective turnover time is revisited with a focus on the sole contribution of magnetic activity to the Ca II H&K emission, the so-called excess flux, and its dimensionless indicator R+HK in relation to other stellar parameters and activity indicators. Our study is based on a sample of 169 main-sequence stars with directly measured Mount Wilson S-indices and rotation periods. The R+HK values are derived from the respective S-indices and related to the rotation periods in various B–V-colour intervals. First, we show that stars with vanishing magnetic activity, i.e. stars whose excess flux index R+HK approaches zero, have a well-defined, colour-dependent rotation period distribution; we also show that this rotation period distribution applies to large samples of cool stars for which rotation periods have recently become available. Second, we use empirical arguments to equate this rotation period distribution with the global convective turnover time, which is an approach that allows us to obtain clear relations between the magnetic activity related excess flux index R+HK, rotation periods, and Rossby numbers. Third, we show that the activity versus Rossby number relations are very similar in the different activity indicators. As a consequence of our study, we emphasize that our Rossby number based on the global convective turnover time approaches but does not exceed unity even for entirely inactive stars. Furthermore, the rotation-activity relations might be universal for different activity indicators once the proper scalings are used.