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Title: Kepler monitoring of an L dwarf I. The photometric period and white light flares

We report on the results of 15 months of monitoring the nearby field L1 dwarf WISEP J190648.47+401106.8 (W1906+40) with the Kepler mission. Supporting observations with the Karl G. Jansky Very Large Array and Gemini North Telescope reveal that the L dwarf is magnetically active, with quiescent radio and variable Hα emission. A preliminary trigonometric parallax shows that W1906+40 is at a distance of 16.35{sub −0.34}{sup +0.36} pc, and all observations are consistent with W1906+40 being an old disk star just above the hydrogen-burning limit. The star shows photometric variability with a period of 8.9 hr and an amplitude of 1.5%, with a consistent phase throughout the year. We infer a radius of 0.92 ± 0.07R{sub J} and sin i > 0.57 from the observed period, luminosity (10{sup –3.67} {sup ±} {sup 0.03} L {sub ☉}), effective temperature (2300 ± 75 K), and vsin i (11.2 ± 2.2 km s{sup –1}). The light curve may be modeled with a single large, high latitude dark spot. Unlike many L-type brown dwarfs, there is no evidence of other variations at the ≳ 2% level, either non-periodic or transient periodic, that mask the underlying rotation period. We suggest that the long-lived surface features maymore » be due to starspots, but the possibility of cloud variations cannot be ruled out without further multi-wavelength observations. During the Gemini spectroscopy, we observed the most powerful flare ever seen on an L dwarf, with an estimated energy of ∼1.6 × 10{sup 32} erg in white light emission. Using the Kepler data, we identify similar flares and estimate that white light flares with optical/ultraviolet energies of 10{sup 31} erg or more occur on W1906+40 as often as 1-2 times per month.« less
Authors:
 [1] ;  [2] ; ;  [3] ;  [4] ;  [5] ;  [6]
  1. Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)
  2. Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States)
  3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  4. US Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Road, Flagstaff, AZ 86001 (United States)
  5. Department of Physics and Astronomy, Hunter College, City University of New York, 695 Park Avenue, New York, NY 10065 (United States)
  6. Department of Physics and Astronomy, State University of New York, Stony Brook, NY 11794 (United States)
Publication Date:
OSTI Identifier:
22348386
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; 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; AMPLITUDES; DWARF STARS; EMISSION; HYDROGEN BURNING; LUMINOSITY; PERIODICITY; PHOTOMETRY; ROTATION; SPECTROSCOPY; STARS; STARSPOTS; SURFACES; TELESCOPES; TRANSIENTS; ULTRAVIOLET RADIATION; VISIBLE RADIATION; WAVELENGTHS