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arXiv 2102.12504astro-ph.SR
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FUMES。II。年轻活跃M矮星的Ly $α$重建

FUMES. II. Ly$α$ Reconstructions of Young, Active M Dwarfs

Allison Youngblood, J. Sebastian Pineda, Kevin France

备注：
Accepted to AAS Journals, Paper 2 of series
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摘要：

HI Ly $α$（1215.67 $\unicode{xC5}$）发射线在M矮星的远紫外光谱中占主导地位，但星际介质中中性氢的强烈吸收使得即使是最近的恒星也难以观测到Ly $α$。作为远紫外线M矮星演化巡天（FUMES）的一部分，哈勃太空望远镜观测了10个早期到中期的M矮星，年龄从$\sim$ 2400万年到几个陀螺，以评估入射紫外线辐射如何在系外行星系统的生命周期中演化。我们从STIS G140 L和E140 M光谱中重建了本征赖氨酸$α$分布，并获得了重建通量，其中1- $σ$不确定度对于低分辨率光谱（G140 L）为5%到2倍，对于高分辨率光谱（E140 M）为3-20%。我们观察广泛的，500-1000公里的$^{-1}$翅膀的LY $α$线的轮廓，并分析如何线宽取决于恒星的属性。我们发现恒星有效温度和表面重力是影响线宽的主要因素，恒星磁活动水平对线宽的影响很小，Ly $α$翼的表面通量密度可以用来估算色球层电子密度. G140 L光谱上的Ly $α$重建是首次尝试在$λ/Δλ\sim$ 1000数据上进行。我们发现，重建精度与观测信噪比无关，而取决于恒星Ly $α$线的本征宽度。年轻的低重力恒星具有最宽的谱线，因此在低光谱分辨率下提供更多的信息，以打破模型参数之间的简并。

英文摘要：

The HI Ly$α$ (1215.67 $\unicode{xC5}$) emission line dominates the far-UV spectra of M dwarf stars, but strong absorption from neutral hydrogen in the interstellar medium makes observing Ly$α$ challenging even for the closest stars. As part of the Far-Ultraviolet M-dwarf Evolution Survey (FUMES), the Hubble Space Telescope has observed 10 early-to-mid M dwarfs with ages ranging from $\sim$24 Myr to several Gyrs to evaluate how the incident UV radiation evolves through the lifetime of exoplanetary systems. We reconstruct the intrinsic Ly$α$ profiles from STIS G140L and E140M spectra and achieve reconstructed fluxes with 1-$σ$ uncertainties ranging from 5% to a factor of two for the low resolution spectra (G140L) and 3-20% for the high resolution spectra (E140M). We observe broad, 500-1000 km s$^{-1}$ wings of the Ly$α$ line profile, and analyze how the line width depends on stellar properties. We find that stellar effective temperature and surface gravity are the dominant factors influencing the line width with little impact from the star's magnetic activity level, and that the surface flux density of the Ly$α$ wings may be used to estimate the chromospheric electron density. The Ly$α$ reconstructions on the G140L spectra are the first attempted on $λ/Δλ\sim$1000 data. We find that the reconstruction precision is not correlated with SNR of the observation, rather, it depends on the intrinsic broadness of the stellar Ly$α$ line. Young, low-gravity stars have the broadest lines and therefore provide more information at low spectral resolution to the fit to break degeneracies among model parameters.

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