高速G、K和M矮星的内禀莱曼α轮廓
Intrinsic Lyman alpha Profiles of High-Velocity G, K, and M Dwarfs
摘要：
观测H I Lyman alpha是晚型恒星最亮的紫外线发射线，对于理解恒星色球和过渡区、模拟系外行星大气中的光化学以及测量星际介质中中性氢和氘的丰度至关重要。然而，由于星际气体的严重衰减，莱曼α观测是众所周知的挑战，阻碍了我们对这一重要发射线基本形态的理解。我们提出了高分辨率的远紫外和近紫外光谱的五个G，K和M矮星的径向速度大到足以多普勒频移恒星莱曼α发射线远离大部分的星际衰减，允许线核心直接观察。我们检测到自反转的莱曼α发射线核心的所有目标，我们表明，自反转的深度随着表面重力的增加而减小。Mg II自反转发射线轮廓提供了一些有用的信息来约束莱曼α线核心，但差异是足够显著的Mg II不能直接用作内在莱曼α模板在重建过程中。我们发现，重建忽略自反转可以高估高达60%-100%的G和K矮星和40%-170%的M矮星的内在莱曼α通量。我们样本中的五颗恒星具有低磁活动和太阳下金属丰度;需要更大的样本量来确定这些结果对这些因素的敏感程度。
英文摘要：
Observations of H I Lyman alpha, the brightest UV emission line of late-type stars, are critical for understanding stellar chromospheres and transition regions, modeling photochemistry in exoplanet atmospheres, and measuring the abundances of neutral hydrogen and deuterium in the interstellar medium. Yet, Lyman alpha observations are notoriously challenging due to severe attenuation from interstellar gas, hindering our understanding of this important emission line's basic morphology. We present high-resolution far- and near-UV spectroscopy of five G, K, and M dwarfs with radial velocities large enough to Doppler shift the stellar Lyman alpha emission line away from much of the interstellar attenuation, allowing the line core to be directly observed. We detect self-reversal in the Lyman alpha emission line core for all targets, and we show that the self-reversal depth decreases with increasing surface gravity. Mg II self-reversed emission line profiles provide some useful information to constrain the Lyman alpha line core, but the differences are significant enough that Mg II cannot be used directly as an intrinsic Lyman alpha template during reconstructions. We show that reconstructions that neglect self-reversal could overestimate intrinsic Lyman alpha fluxes by as much as 60%-100% for G and K dwarfs and 40%-170% for M dwarfs. The five stars of our sample have low magnetic activity and sub-solar metallicity; a larger sample size is needed to determine how sensitive these results are to these factors.
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