Magnetic Inflation and Stellar Mass. V. Intensification and Saturation of M-dwarf Absorption Lines with Rossby Number
Magnetic Inflation and Stellar Mass. V. Intensification and Saturation of M-dwarf Absorption Lines with Rossby Number
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DOI：
10.3847/1538-3881/ab5d3d
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发表时间：
2019-12
期刊：
影响因子：
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通讯作者：
P. Muirhead;M. Veyette;E. Newton;C. Theissen;A. Mann
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文献类型：
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作者：
P. Muirhead;M. Veyette;E. Newton;C. Theissen;A. Mann
在年轻的类太阳恒星和M-矮星中，色球和日冕磁活动指标，如Hα、X射线和射电辐射，已知在低罗斯比数（Ro = 0.1）下饱和，定义为自转周期与对流周转时间的比值。饱和的机制尚不清楚。本文利用Y波段的光球Ti i和Ca i吸收线研究了Rossby数在0.01 ~ 1.0之间的M矮星的磁场强度。这些线的等效宽度被光球斑、全球场或两者的结合所磁增强。等效宽度的表现在性质上与色球和日冕指标相似：我们看到等效宽度随着Ro的减小而增加（吸收增加），并且当Ro> 0.1时等效宽度饱和。本研究中的大多数M矮星都是完全对流的。这些结果增加了越来越多的证据，证明磁饱和机制发生在恒星光球层或其下。
In young Sun-like stars and field M-dwarf stars, chromospheric and coronal magnetic activity indicators such as Hα, X-ray, and radio emission are known to saturate with low Rossby number (Ro ≲ 0.1), defined as the ratio of rotation period to convective turnover time. The mechanism for the saturation is unclear. In this paper, we use photospheric Ti i and Ca i absorption lines in the Y band to investigate magnetic field strength in M dwarfs for Rossby numbers between 0.01 and 1.0. The equivalent widths of the lines are magnetically enhanced by photospheric spots, a global field, or a combination of the two. The equivalent widths behave qualitatively similar to the chromospheric and coronal indicators: we see increasing equivalent widths (increasing absorption) with decreasing Ro and saturation of the equivalent widths for Ro ≲ 0.1. The majority of M dwarfs in this study are fully convective. The results add to mounting evidence that the magnetic saturation mechanism occurs at or beneath the stellar photosphere.