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The HI Ly$alpha$ (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$alpha$ 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$24 Myr to several Gyrs to evaluate how the incident UV radiation evolves through the lifetime of exoplanetary systems. We reconstruct the intrinsic Ly$alpha$ profiles from STIS G140L and E140M spectra and achieve reconstructed fluxes with 1-$sigma$ 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$alpha$ 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 stars magnetic activity level, and that the surface flux density of the Ly$alpha$ wings may be used to estimate the chromospheric electron density. The Ly$alpha$ reconstructions on the G140L spectra are the first attempted on $lambda/Deltalambdasim$1000 data. We find that the reconstruction precision is not correlated with SNR of the observation, rather, it depends on the intrinsic broadness of the stellar Ly$alpha$ 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.
[Abridged] We present the first comprehensive study of short-timescale chromospheric H-alpha variability in M dwarfs using the individual 15 min spectroscopic exposures for 52,392 objects from the Sloan Digital Sky Survey. Our sample contains about 1
Traces of photospheric hydrogen are detected in at least half of all white dwarfs with helium-dominated atmospheres through the presence of H alpha in high-quality optical spectroscopy. Previous studies have noted significant discrepancies between th
We image 104 newly identified low-mass (mostly M-dwarf) pre-main sequence members of nearby young moving groups with Magellan Adaptive Optics (MagAO) and identify 27 binaries with instantaneous projected separation as small as 40 mas. 15 were previou
M dwarf stars are excellent candidates around which to search for exoplanets, including temperate, Earth-sized planets. To evaluate the photochemistry of the planetary atmosphere, it is essential to characterize the UV spectral energy distribution of
A large sample of over 38,000 chromospherically active candidate solar-like stars and cooler dwarfs from the RAVE survey is addressed in this paper. An improved activity identification with respect to the previous study was introduced to build a cata