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Title: HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive

Abstract

The ultraviolet (UV) light from a host star influences a planet’s atmospheric photochemistry and will affect interpretations of exoplanetary spectra from future missions like the James Webb Space Telescope . These effects will be particularly critical in the study of planetary atmospheres around M dwarfs, including Earth-sized planets in the habitable zone. Given the higher activity levels of M dwarfs compared to Sun-like stars, time-resolved UV data are needed for more accurate input conditions for exoplanet atmospheric modeling. The Galaxy Evolution Explorer ( GALEX ) provides multi-epoch photometric observations in two UV bands: near-ultraviolet (NUV; 1771–2831 Å) and far-ultraviolet (FUV; 1344–1786 Å). Within 30 pc of Earth, there are 357 and 303 M dwarfs in the NUV and FUV bands, respectively, with multiple GALEX observations. Simultaneous NUV and FUV detections exist for 145 stars in both GALEX bands. Our analyses of these data show that low-mass stars are typically more variable in the FUV than the NUV. Median variability increases with later spectral types in the NUV with no clear trend in the FUV. We find evidence that flares increase the FUV flux density far more than the NUV flux density, leading to variable FUV to NUV flux density ratiosmore » in the GALEX bandpasses.The ratio of FUV to NUV flux is important for interpreting the presence of atmospheric molecules in planetary atmospheres such as oxygen and methane as a high FUV to NUV ratio may cause false-positive biosignature detections. This ratio of flux density in the GALEX bands spans three orders of magnitude in our sample, from 0.008 to 4.6, and is 1 to 2 orders of magnitude higher than for G dwarfs like the Sun. These results characterize the UV behavior for the largest set of low-mass stars to date.« less

Authors:
 [1];  [2]
  1. Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
  2. School of Earth and Space Exploration, Arizona State University, 781 S Terrace Road, Tempe, AZ 85281 (United States)
Publication Date:
OSTI Identifier:
22663355
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 154; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPARATIVE EVALUATIONS; DWARF STARS; FAR ULTRAVIOLET RADIATION; FLUX DENSITY; GALACTIC EVOLUTION; GALAXIES; MASS; METHANE; MOLECULES; NEAR ULTRAVIOLET RADIATION; OXYGEN; PHOTOCHEMISTRY; PLANETARY ATMOSPHERES; PLANETS; SPACE; SUN; TELESCOPES

Citation Formats

Miles, Brittany E., and Shkolnik, Evgenya L., E-mail: bmiles@ucsc.edu. HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA71AB.
Miles, Brittany E., & Shkolnik, Evgenya L., E-mail: bmiles@ucsc.edu. HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive. United States. doi:10.3847/1538-3881/AA71AB.
Miles, Brittany E., and Shkolnik, Evgenya L., E-mail: bmiles@ucsc.edu. Tue . "HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive". United States. doi:10.3847/1538-3881/AA71AB.
@article{osti_22663355,
title = {HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive},
author = {Miles, Brittany E. and Shkolnik, Evgenya L., E-mail: bmiles@ucsc.edu},
abstractNote = {The ultraviolet (UV) light from a host star influences a planet’s atmospheric photochemistry and will affect interpretations of exoplanetary spectra from future missions like the James Webb Space Telescope . These effects will be particularly critical in the study of planetary atmospheres around M dwarfs, including Earth-sized planets in the habitable zone. Given the higher activity levels of M dwarfs compared to Sun-like stars, time-resolved UV data are needed for more accurate input conditions for exoplanet atmospheric modeling. The Galaxy Evolution Explorer ( GALEX ) provides multi-epoch photometric observations in two UV bands: near-ultraviolet (NUV; 1771–2831 Å) and far-ultraviolet (FUV; 1344–1786 Å). Within 30 pc of Earth, there are 357 and 303 M dwarfs in the NUV and FUV bands, respectively, with multiple GALEX observations. Simultaneous NUV and FUV detections exist for 145 stars in both GALEX bands. Our analyses of these data show that low-mass stars are typically more variable in the FUV than the NUV. Median variability increases with later spectral types in the NUV with no clear trend in the FUV. We find evidence that flares increase the FUV flux density far more than the NUV flux density, leading to variable FUV to NUV flux density ratios in the GALEX bandpasses.The ratio of FUV to NUV flux is important for interpreting the presence of atmospheric molecules in planetary atmospheres such as oxygen and methane as a high FUV to NUV ratio may cause false-positive biosignature detections. This ratio of flux density in the GALEX bands spans three orders of magnitude in our sample, from 0.008 to 4.6, and is 1 to 2 orders of magnitude higher than for G dwarfs like the Sun. These results characterize the UV behavior for the largest set of low-mass stars to date.},
doi = {10.3847/1538-3881/AA71AB},
journal = {Astronomical Journal (Online)},
number = 2,
volume = 154,
place = {United States},
year = {Tue Aug 01 00:00:00 EDT 2017},
month = {Tue Aug 01 00:00:00 EDT 2017}
}