The High-energy Spectrum of the Nearby Planet-hosting Inactive Mid-M Dwarf LHS 3844

• Published in: The Astronomical journal 2021-07, Vol.162 (1), p.10
• Main Authors: Diamond-Lowe, Hannah, Youngblood, Allison, Charbonneau, David, King, George, Teal, D. J., Bastelberger, Sandra, Corrales, Lia, Kempton, Eliza M.-R.
• Format: Article
• Language: English
• Subjects: Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BOLOMETERS; EARTH PLANET; EMISSION; Emissions; Energy; Energy flux; ENERGY SPECTRA; Exoplanet atmospheres; Extrasolar planets; EXTREME ULTRAVIOLET RADIATION; Fluctuations; Flux; Hubble Space Telescope; Interstellar matter; Interstellar medium; LUMINOSITY; M dwarf stars; Muscles; NUCLEAR PHYSICS AND RADIATION PHYSICS; Planetary orbits; Radiation; Red dwarf stars; SOFT X RADIATION; Soft x rays; Space observatories; STARS; Stellar flares; Terrestrial environments; Terrestrial planets; Ultraviolet astronomy; Ultraviolet observatories; ULTRAVIOLET SPECTRA; X-ray fluxes
• ISSN: 0004-6256; 1538-3881; 1538-3881
• DOI: 10.3847/1538-3881/abfa1c

To fully characterize the atmospheres, or lack thereof, of terrestrial exoplanets, we must include the high-energy environments provided by their host stars. The nearby mid-M dwarf LHS 3844 hosts a terrestrial world that lacks a substantial atmosphere. We present a time-series UV spectrum of LHS 3844 from 1131 to 3215 Å captured by HST/COS. We detect one flare in the FUV that has an absolute energy of 8.96 ± 0.77 × 10 28 erg and an equivalent duration of 355 ± 31 s. We extract the flare and quiescent UV spectra separately. For each spectrum, we estimate the Ly α flux using correlations between UV line strengths. We use Swift-XRT to place an upper limit on the soft X-ray flux and construct a differential emission model to estimate flux that is obscured by the interstellar medium. We compare the differential emission model flux estimates in the XUV to other methods that rely on scaling from the Ly α , Si iv , and N v lines in the UV. The XUV, FUV, and NUV flux of LHS 3844 relative to its bolometric luminosity is log 10 ( L band / L Bol ) =−3.65, −4.16, and −4.48, respectively, for the quiescent state. These values agree with trends in high-energy flux as a function of stellar effective temperature found by the MUSCLES survey for a sample of early-M dwarfs. Many of the most spectroscopically accessible terrestrial exoplanets orbit inactive mid-to-late M dwarfs like LHS 3844. Measurements of M dwarf high-energy spectra are preferable for exoplanet characterization but are not always possible. The spectrum of LHS 3844 is a useful proxy for the current radiation environment for these worlds.