The H i Lyα (1215.67 Å) emission line dominates the far-UV spectra of M dwarf stars, but strong absorption from neutral hydrogen in the interstellar medium makes observing Lyα challenging even for the closest stars. As part of the Far-Ultraviolet M-dwarf Evolution Survey, the Hubble Space Telescope has observed 10 early-to-mid M dwarfs with ages ranging from ∼24 Myr to several Gyr in order to evaluate how the incident UV radiation evolves through the lifetime of exoplanetary systems. We reconstruct the intrinsic Lyα profiles from STIS G140L and E140M spectra, and achieve reconstructed fluxes with 1σ 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 Lyα 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 Lyα wings may be used to estimate the chromospheric electron density. The Lyα reconstructions on the G140L spectra are the first attempted on λ/Δλ ∼ 1000 data. We find that the reconstruction precision is not correlated with the signal-to-noise ratio of the observation—rather, it depends on the intrinsic broadness of the stellar Lyα 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.

H i Ly α (1215.67 Å) 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对于最近的恒星也难以观测 Ly α。作为远紫外 M 矮星演化调查的一部分，哈勃太空望远镜观测了 10 个早中期 M 矮星，其年龄范围从 ~24 Myr 到几 Gyr 不等，以评估入射紫外线辐射如何在整个生命周期中演化系外行星系统。我们从 STIS G140L 和 E140M 光谱重建本征 Ly α剖面，并获得 1 σ 的重建通量低分辨率光谱 (G140L) 和高分辨率光谱 (E140M) 的不确定性范围为 5% 到 2 倍。我们观察到 Ly α线剖面的宽 500-1000 km s ^-1翼，并分析线宽如何取决于恒星特性。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，受恒星磁活动水平的影响很小，并且Ly α翼的表面通量密度可用于估计色球电子密度。G140L 光谱上的Ly α重建是首次尝试对λ /Δ λ∼ 1000 条数据。我们发现重建精度与观测的信噪比无关，而是取决于恒星 Ly α线的内在宽度。年轻的低重力恒星具有最宽的谱线，因此可以在低光谱分辨率下提供更多信息以进行拟合，以打破模型参数之间的简并性。