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Published January 1, 2015 | Submitted + Published
Journal Article Open

The Near-ultraviolet Luminosity Function of Young, Early M-type Dwarf Stars


Planets orbiting within the close-in habitable zones of M dwarf stars will be exposed to elevated high-energy radiation driven by strong magnetohydrodynamic dynamos during stellar youth. Near-ultraviolet (NUV) irradiation can erode and alter the chemistry of planetary atmospheres, and a quantitative description of the evolution of NUV emission from M dwarfs is needed when modeling these effects. We investigated the NUV luminosity evolution of early M-type dwarfs by cross-correlating the Lépine & Gaidos catalog of bright M dwarfs with the Galaxy Evolution Explorer (GALEX) catalog of NUV (1771-2831 angstrom) sources. Of the 4805 sources with GALEX counterparts, 797 have NUV emission significantly (>2.5 sigma) in excess of an empirical basal level. We inspected these candidate active stars using visible-wavelength spectra, high-resolution adaptive optics imaging, time-series photometry, and literature searches to identify cases where the elevated NUV emission is due to unresolved background sources or stellar companions; we estimated the overall occurrence of these "false positives" (FPs) as similar to 16%. We constructed an NUV luminosity function that accounted for FPs, detection biases of the source catalogs, and GALEX upper limits. We found the NUV luminosity function to be inconsistent with predictions from a constant star-formation rate and simplified age-activity relation defined by a two-parameter power law.

Additional Information

© 2015 American Astronomical Society. Received 2014 July 23; accepted 2014 October 22; published 2014 December 18. M.A. and E.G. acknowledge support from NASA Grants NNX10AQ36G (Astrobiology: Exobiology and Evolutionary Biology) and NNX11AC33G (Origins of Solar System). This research utilized the NASA Astrophysics Data System, SIMBAD database, and Vizier catalogue access tool. It also made use of the AAVSO Photometric All-Sky Survey, funded by the Robert Martin Ayers Sciences Fund. We thank the dedicated staff of the UH88, MDM, SAAO, and CASLEO observatories from which many spectra were obtained for this work. We especially thank Greg Aldering for years of assistance with SNIFS on the UH88. We also thank Evgenya Shkolnik for her very useful comments regarding GALEX. This paper used observations taken with the Robo-AO system. The Robo-AO system is supported by collaborating partner institutions, the California Institute of Technology and the Inter-University Centre for Astronomy and Astrophysics, by the National Science Foundation under Grants AST-0906060, AST-0960343, and AST-1207891, by a grant from the Mt. Cuba Astronomical Foundation, and by a gift from Samuel Oschin. C.B. acknowledges support from the Alfred P. Sloan Foundation.

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Published - 0004-637X_798_1_41.pdf

Submitted - 1410.6488v1.pdf


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