Journal article
H-2 Fluorescence in M Dwarf Systems: A Stellar Origin
The Astrophysical journal, Vol.845(1), p.3
07/04/2017
DOI: 10.3847/1538-4357/aa7b79
Abstract
Observations of molecular hydrogen (H-2) fluorescence are a potentially useful tool for measuring the H-2 abundance in exoplanet atmospheres. This emission was previously observed in M dwarfs with planetary systems. However, low signal-to-noise prevented a conclusive determination of its origin. Possible sources include exoplanetary atmospheres, circumstellar gas disks, and the stellar surface. We use observations from the "Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanet Host Stars" Treasury Survey to study H-2 fluorescence in M dwarfs. We detect fluorescence in Hubble Space Telescope spectra of 8/9 planet-hosting and 5/6 non-planet- hosting M dwarfs. The detection statistics, velocity centroids, and line widths of the emission suggest a stellar origin. We calculate H-2-to-stellar-ion flux ratios to compare flux levels between stars. For stars with planets, we find an average ratio of 1.7 +/- 0.9, using the fluxes of the brightest H-2 feature and two stellar C IV lines. This is compared to 0.9 +/- 0.4 for stars without planets, showing that the planet-hosting M dwarfs do not have significant excess H-2 emission. This claim is supported by the direct FUV imaging of GJ 832, where no fluorescence is observed at the expected star-planet separation. Additionally, the 3 sigma upper limit of 4.9 x 10(-17) erg cm(-2) s(-1) from these observations is two orders of magnitude below the spectroscopically observed H-2 flux. We constrain the location of the fluorescing H-2 using 1D radiative transfer models, and find that it could reside in starspots or a similar to 2500-3000 K region in the lower chromosphere. The presence of this emission could complicate efforts to quantify the atmospheric abundance of H-2 in exoplanets orbiting M dwarfs.
Details
- Title: Subtitle
- H-2 Fluorescence in M Dwarf Systems: A Stellar Origin
- Creators
- Nicholas Kruczek - Laboratory for Atmospheric and Space PhysicsKevin France - Univ Colorado, Lab Atmospher & Space Phys, 600 UCB, Boulder, CO 80309 USAWilliam Evonosky - University of South FloridaR. O. Parke Loyd - Laboratory for Atmospheric and Space PhysicsAllison Youngblood - Laboratory for Atmospheric and Space PhysicsAki Roberge - Goddard Space Flight CenterRobert A. Wittenmyer - UNSW SydneyJohn T. Stocke - Laboratory for Atmospheric and Space PhysicsBrian Fleming - Laboratory for Atmospheric and Space PhysicsKeri Hoadley - Laboratory for Atmospheric and Space Physics
- Resource Type
- Journal article
- Publication Details
- The Astrophysical journal, Vol.845(1), p.3
- Publisher
- Iop Publishing Ltd
- DOI
- 10.3847/1538-4357/aa7b79
- ISSN
- 0004-637X
- eISSN
- 1538-4357
- Number of pages
- 15
- Grant note
- 13650; 14100 / HST Guest Observing programs 1120459 / Directorate For Geosciences; National Science Foundation (NSF); NSF - Directorate for Geosciences (GEO) 089.C-0904(A) / European Organisation for Astronomical Research in the Southern Hemisphere, under ESO programme AGS-1120459 / Significant Opportunities in Atmospheric Research and Science (SOARS) program, NSF grant
- Language
- English
- Date published
- 07/04/2017
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984429057302771
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