2016/04/04 by Allison Youngblood, Kevin France, R. O. Parke Loyd +9 · 15 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Extreme ultraviolet #Flux (metallurgy) #Interstellar medium #Ionization #Line (geometry) #Monte Carlo method #Spectral line #Stars #Stellar, planetary, and galactic studies #Ultraviolet #astro-ph.SR
paper · pdf · doi:10.3847/0004-637x/824/2/101
20 pages, 9 figures, accepted for publication in ApJ
arxiv created 2016/04/04 · openalex publication_date 2016/06/20 · openalex created_date 2016/06/24 · arxiv updated 2016/06/29 · openalex updated_date 2026/08/05
ABSTRACT The ultraviolet (UV) spectral energy distributions (SEDs) of low-mass (K- and M-type) stars play a critical role in the heating and chemistry of exoplanet atmospheres, but are not observationally well-constrained. Direct observations of the intrinsic flux of the Ly α line (the dominant source of UV photons from low-mass stars) are challenging, as interstellar H i absorbs the entire line core for even the closest stars. To address the existing gap in empirical constraints on the UV flux of K and M dwarfs, the MUSCLES Hubble Space Telescope Treasury Survey has obtained UV observations of 11 nearby M and K dwarfs hosting exoplanets. This paper presents the Ly α and extreme-UV spectral reconstructions for the MUSCLES targets. Most targets are optically inactive, but all exhibit significant UV activity. We use a Markov Chain Monte Carlo technique to correct the observed Ly α profiles for interstellar absorption, and we employ empirical relations to compute the extreme-UV SED from the intrinsic Ly α flux in ∼100 Å bins from 100–1170 Å. The reconstructed Ly α profiles have 300 km s −1 broad cores, while >1% of the total intrinsic Ly α flux is measured in extended wings between 300 and 1200 km s −1 . The Ly α surface flux positively correlates with the Mg ii surface flux and negatively correlates with the stellar rotation period. Stars with larger Ly α surface flux also tend to have larger surface flux in ions formed at higher temperatures, but these correlations remain statistically insignificant in our sample of 11 stars. We also present H i column density measurements for 10 new sightlines through the local interstellar medium.