Rotation and differential rotation of active Kepler stars
Rotation and differential rotation of active Kepler stars
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DOI：
10.1051/0004-6361/201321970
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发表时间：
2013-08
影响因子：
6.5
通讯作者：
T. Reinhold;A. Reiners;G. Basri
中科院分区：
文献类型：
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作者：
T. Reinhold;A. Reiners;G. Basri
我们从Q3数据中得出了开普勒场中数千颗活跃恒星的自转周期。在大多数情况下，检测到接近旋转周期的第二个周期，我们将其解释为表面微分旋转（DR）。利用变幅范围从整个样本中选取活动恒星。为了检测光曲线中的不同周期，我们在预白化方法中使用Lomb-Scargle周期图来获得全局正弦拟合的参数。拟合中最主要的时期归因于不同的地表旋转周期，但斑点演化也可能起作用。由于恒星数量多，周期误差用统计方法估计。因此，我们不能排除在我们的时期中存在假阳性。在40.661颗活跃恒星的样本中，我们发现24.124个自转周期$P_1$在0.5-45天之间。0.5 < B-V < 1.0和年龄小于300 Myr的角动量演化恒星的分布与恒定的恒星形成速率一致。第二个周期$P_2$在里面 $\pm30$% of the rotation period $P_1$ was found in 18.619 stars (77.2%). Attributing these two periods to DR we found that the relative shear $\alpha=\Delta\Omega/\Omega$ increases with rotation period, and slightly decreases with effective temperature. The absolute shear $\Delta\Omega$ slightly increases between $T_{eff}=3500-6000$ K. Above 6000 K $\Delta\Omega$ shows much larger scatter. We found weak dependence of $\Delta\Omega$ on rotation period. Latitudinal differential rotation measured for the first time in more than 18.000 stars provides a comprehensive picture of stellar surface shear, consistent with major predictions from mean-field theory. To what extent our observations are prone to false positives and selection bias is not fully explored, and needs to be addressed using more Kepler data.
We present rotation periods for thousands of active stars in the Kepler field derived from Q3 data. In most cases a second period close to the rotation period was detected, which we interpreted as surface differential rotation (DR). Active stars were selected from the whole sample using the range of the variability amplitude. To detect different periods in the light curves we used the Lomb-Scargle periodogram in a pre-whitening approach to achieve parameters for a global sine fit. The most dominant periods from the fit were ascribed to different surface rotation periods, but spot evolution could also play a role. Due to the large number of stars the period errors were estimated in a statistical way. We thus cannot exclude the existence of false positives among our periods. In our sample of 40.661 active stars we found 24.124 rotation periods $P_1$ between 0.5-45 days. The distribution of stars with 0.5 < B-V < 1.0 and ages derived from angular momentum evolution that are younger than 300 Myr is consistent with a constant star-formation rate. A second period $P_2$ within $\pm30$% of the rotation period $P_1$ was found in 18.619 stars (77.2%). Attributing these two periods to DR we found that the relative shear $\alpha=\Delta\Omega/\Omega$ increases with rotation period, and slightly decreases with effective temperature. The absolute shear $\Delta\Omega$ slightly increases between $T_{eff}=3500-6000$ K. Above 6000 K $\Delta\Omega$ shows much larger scatter. We found weak dependence of $\Delta\Omega$ on rotation period. Latitudinal differential rotation measured for the first time in more than 18.000 stars provides a comprehensive picture of stellar surface shear, consistent with major predictions from mean-field theory. To what extent our observations are prone to false positives and selection bias is not fully explored, and needs to be addressed using more Kepler data.