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Time-Resolved Ultraviolet Spectroscopy of The M-Dwarf GJ 876 Exoplanetary SystemExtrasolar planets orbiting M-stars may represent our best chance to discover habitable worlds in the coming decade. The ultraviolet spectrum incident upon both Earth-like and Jovian planets is critically important for proper modeling of their atmospheric heating and chemistry. In order to provide more realistic inputs for atmospheric models of planets orbiting low-mass stars, we present new near- and far-ultraviolet (NUV and FUV) spectroscopy of the M-dwarf exoplanet host GJ 876 (M4V). Using the COS and STIS spectrographs on board the Hubble Space Telescope, we have measured the 1150-3140 A spectrum of GJ 876. We have reconstructed the stellar H1 Ly alpha emission line profile, and find that the integrated Ly alpha flux is roughly equal to the rest of the integrated flux (1150-1210 A + 1220-3140 A) in the entire ultraviolet bandpass (F(Ly alpha)/F(FUV+NUV) equals approximately 0.7). This ratio is approximately 2500x greater than the solar value. We describe the ultraviolet line spectrum and report surprisingly strong fluorescent emission from hot H2 (T(H2) greater than 2000 K). We show the light curve of a chromospheric + transition region flare observed in several far-UV emission lines, with flare/quiescent flux ratios greater than or equal to 10. The strong FUV radiation field of an M-star (and specifically Ly alpha) is important for determining the abundance of O2--and the formation of biomarkers-in the lower atmospheres of Earth-like planets in the habitable zones of low-mass stars.
Document ID
Document Type
Reprint (Version printed in journal)
France, Kevin (Colorado Univ. Boulder, CO, United States)
Linsky, Jeffrey L. (Colorado Univ. Boulder, CO, United States)
Tian, Feng (Colorado Univ. Boulder, CO, United States)
Froning, Cynthia S. (Colorado Univ. Boulder, CO, United States)
Roberge, Aki (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 25, 2013
Publication Date
May 10, 2012
Publication Information
Publication: The Astrophysical Journal Letters
Volume: 750
Issue: 2
Subject Category
Report/Patent Number
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