The Detection of M Dwarf UV Flare Events in the GALEX Data Archives

Creators: Welsh, Barry Y.; Wheatley, Jonathan M.; Seibert, Mark; Browne, Stanley E.; West, Andrew A.; Siegmund, Oswald H. W.; Barlow, Tom A.; Forster, Karl; Friedman, Peter G.; Martin, D. Christopher; Morrissey, Patrick; Small, Todd; Wyder, Ted; Schiminovich, David

Abstract

We present the preliminary results from implementing a new software tool that enables inspection of time-tagged photon data for the astronomical sources contained within individual GALEX ultraviolet (UV) images of the sky. We have inspected the photon data contained within 1802 GALEX images to reveal rapid, short-term (≲500 s) UV source variability in the form of stellar "flares." The mean associated change in near-UV (NUV) magnitude due to this flaring activity is 2.7 ± 0.3 mag. A list of 49 new UV variable star candidates is presented, together with their associated Sloan Digital Sky Survey (SDSS) photometric magnitudes. From these data we can associate the main source of these UV flare events with magnetic activity on M dwarf stars. Photometric parallaxes have been determined for 32 of these sources, placing them at distances ranging from approximately 25 to 1000 pc. The average UV flare energy for these flare events is 2.5 × 10^(30) ergs, which is of a similar energy to that of U-band, X-ray, and EUV flares observed on many local M dwarf stars. We have found that stars of classes M0 to M5 flare with energies spanning a far larger range and with an energy approximately 5 times greater than those of later (M6 to M8) spectral type.

Additional Information

© 2007 American Astronomical Society. Print publication: Issue 2 (2007 December); received 2006 March 24; accepted for publication 2006 May 12. GALEX (Galaxy Evolution Explorer) is a NASA Small Explorer, launched in 2003April.We gratefully acknowledgeNASA's support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d'Etudes Spatiales of France and the Korean Ministry of Science and Technology.We acknowledge the dedicated team of engineers, technicians, and administrative staff fromJPL/Caltech, Orbital Sciences Corporation, University of California, Berkeley, Laboratoire d'Astrophysique de Marseille, and the other institutions who made this mission possible. Financial support for this research was provided by the NASA GALEX Guest Investigator science program. This publicationmakes use of data products from the SIMBAD database, operated at CDS, Strasbourg, France. Facilities: GALEX

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