Estimates of Active Region Area Coverage through Simultaneous Measurements of the He i λλ 5876 and 10830 Lines
Estimates of Active Region Area Coverage through Simultaneous Measurements of the He i λλ 5876 and 10830 Lines
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通过同时测量 He i λλ 5876 和 10830 线估计活动区域覆盖范围
DOI：
10.3847/1538-4357/aa6a14
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
B. Beeck
中科院分区：
文献类型：
--
作者：
V. Andretta;M. Giampapa;E. Covino;A. Reiners;B. Beeck
同时，高质量地测量了太阳类型恒星样本中的中性氦三重态特征，其频率分别为5876？和10830？这些观测是在La Silla Paranal天文台的ESO望远镜下进行的，程序ID 088.D-0028(A)和MPG Utility Run for Fibre Extended-Range光学光谱仪088.A-9029(A)。这些特征的等效宽度结合色球模型被用来推断斑点外磁区的区域覆盖率或填充因子的分数。我们发现大多数样本的特征是填充因子小于1。然而，最冷的K型矮星和最热、自转速度最快的F型矮星之间存在差异。我们讨论了这些明显反常的结果，发现在K型恒星的情况下，它们是应用最适合太阳的色球模型的产物，而不是应用于具有显著较低TJeff的恒星。F型快速转子的情况可以用当量宽度的测量不确定度来解释，但它们也可能是由于大气中的非磁热分量造成的。除了上面提到的例外，初步结果表明，活动区的平均加热率从一颗恒星到另一颗恒星是相同的，但由于区域覆盖的原因，在空间上综合的、观测到的活动水平有所不同。因此，该样品中活性的差异主要是由于活性区域的填充因子。
Simultaneous, high-quality measurements of the neutral helium triplet features at 5876 Å and 10830 Å in a sample of solar-type stars are presented. The observations were made with ESO telescopes at the La Silla Paranal Observatory under program ID 088.D-0028(A) and MPG Utility Run for Fiber Extended-range Optical Spectrograph 088.A-9029(A). The equivalent widths of these features combined with chromospheric models are utilized to infer the fractional area coverage, or filling factor, of magnetic regions outside of spots. We find that the majority of the sample is characterized by filling factors less than unity. However, discrepancies occur among the coolest K-type and the warmest and most rapidly rotating F-type dwarf stars. We discuss these apparently anomalous results and find that in the case of K-type stars, they are an artifact of the application of chromospheric models best suited to the Sun than to stars with significantly lower Teff. The case of the F-type rapid rotators can be explained by the measurement uncertainties of the equivalent widths, but they may also be due to a non-magnetic heating component in their atmospheres. With the exceptions noted above, preliminary results suggest that the average heating rates in the active regions are the same from one star to the other, differing in the spatially integrated, observed level of activity due to the area coverage. Hence, differences in activity in this sample are mainly due to the filling factor of active regions.
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