TWA 6的多普勒图像和色球光变
Doppler Images and Chromospheric Variability of TWA 6
摘要：
我们提出了多普勒成像和巴耳末线分析的弱线金牛座T星TWA 6。利用这些数据，我们首次尝试测量金牛座T星的差分旋转，并首次探测到这样一颗恒星的弹弓日珥。我们还展示了迄今为止最直接的证据，证明太阳以外的恒星中存在太阳型谱斑。2006年2月11日至13日和2006年2月18日至20日进行了六个晚上的观测，当时光谱是用3.9米英澳望远镜上的UCL Echelle摄谱仪拍摄的。使用最小二乘反卷积，以提高有效的信噪比，我们产生了两个多普勒地图。这些图显示了与其他快速旋转的金牛座T星相似的特征，即一个极斑，更多的斑点从它延伸到赤道。对两种图进行了比较，以测量差异旋转。互相关和参数拟合表明TWA 6没有可检测到的差异旋转。研究了该恒星的巴耳末辐射。平均H-α分布有一个与旋转加宽一致的窄分量和一个延伸到250 km/s的宽分量。H-α的变化表明色球层有与光球层中的斑点共空间的活动区域，类似于在太阳上观察到的“斑”。此外，这颗恒星至少有一个弹弓突出3恒星半径以上的表面-第一次在金牛座T恒星这样的检测。
英文摘要：
We present Doppler imaging and Balmer line analysis of the weak-line T Tauri star TWA 6. Using this data we have made one of the first attempts to measure differential rotation in a T Tauri star, and the first detection of a slingshot prominence in such a star. We also show the most direct evidence to date of the existence of solar-type plages in a star other than the Sun. Observations were made over six nights: 11-13th February 2006 and 18-20th February 2006, when spectra were taken with the UCL Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope. Using least-squares deconvolution to improve the effective signal--to--noise ratio we produced two Doppler maps. These show similar features to maps of other rapidly rotating T Tauri stars, i.e. a polar spot with more spots extending out of it down to equator. Comparison of the two maps was carried out to measure the differential rotation. Cross-correlation and parameter fitting indicates that TWA 6 does not have detectable differential rotation. The Balmer emission of the star was studied. The mean H-alpha profile has a narrow component consistent with rotational broadening and a broad component extending out to 250km/s. The variability in H-alpha suggests that the chromosphere has active regions that are cospatial with the spots in the photosphere, similar to the 'plages' observed on the Sun. In addition the star has at least one slingshot prominence 3 stellar radii above the surface - the first such detection in a T Tauri star.
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