AAS 198th Meeting, June 2001
Session 69. Planet Searchs and Dwarfs
Display, Thursday, June 7, 2001, 9:20am-4:00pm, Exhibit Hall

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[69.06] Discovery of Radio Emission from the Brown Dwarf LP944-20, and Preliminary Results from an Ongoing Survey of Nearby Brown Dwarfs with the VLA

E. Berger (Caltech), S. Ball (NM Tech), K. M. Becker (Oberlin), M. Clarke (Carleton), D. A. Frail (NRAO), T. A. Fukuda (U. of Denver), I. M. Hoffman (U. of NM), R. Mellon (Penn State), E. Momjian (U. of Kentucky), N. W. Murphy (Amherst), S. H. Teng (U. of Maryland), T. Woodruff (Southwestern), B. A. Zauderer (Agnes Scott), R. T. Zavala (NM State U.)

Brown dwarfs are not massive enough to sustain thermonuclear fusion of hydrogen at their centres, but are distinguished from gas-giant planets by their ability to burn deuterium. Brown dwarfs older than 10 Myr are expected to possess short-lived magnetic fields and to emit radio and X-rays only very weakly from their coronae. An X-ray flare was recently detected on the brown dwarf LP944-20, whereas previous searches for optical activity (and one X-ray search) yielded negative results. Here we report the discovery of quiescent and flaring radio emission from LP944-20, with luminosities several orders of magnitude larger than predicted by the empirical relation between the X-ray and radio luminosities that has been found for many types of stars. Interpreting the radio data within the context of synchrotron emission, we show that LP944-20 has an unusually weak magnetic field in comparison to active M-dwarf stars, which might explain the previous null optical and X-ray results, as well as the strength of the radio emissions compared to those at X-ray wavelengths.

In addition, we present preliminary results from an ongoing Very Large Array (VLA) search for radio emission from several nearby brown dwarfs. We show that so far none of the observed sources exhibit emission levels comparable to LP944-20.

Observations of LP944-20 were supported in part by the Research Experience for Undergraduates program of the NSF. The National Radio Astronomy Observatory (NRAO) is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. NRAO operates the VLA.

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