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      The magnetosphere of the ultracool dwarf DENIS 1048-3956

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          Abstract

          Ultracool dwarfs, the least-massive contributors to the stellar mass function, exhibit striking magnetic properties that are inconsistent with trends for more massive stars. Here, we present the widest-band radio observations to date of an ultracool dwarf, DENIS-P J104814.9-395604, in four 2 GHz bandwidths between wavelengths of 1 cm and 10 cm. These data were obtained with the Australia Telescope Compact Array using the new Compact Array Broadband Backend instrument. We detected a stable negatively-sloped power-law spectrum in total intensity, with spectral index alpha=1.71+-0.09. Circular polarization fractions between 0.25 and 0.4 were found at the low-frequency end of our detection band. We interpret these results as indicative of gyrosynchrotron emission. We suggest that the radio emission originates from beyond the co-rotation radius, R_C, of the star. Adopting this model, we find R_C between 1.2-2.9 R_*, and a non-thermal electron density and magnetic field strength between 10^(5)-10^(7.2) cm^(-3) and 70-260 G respectively at R_C. The model accounts for the violation of the Guedel-Benz relation between X-ray and radio luminosities of low-mass stars by DENIS-P J104814.9-395604.

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          Author and article information

          Journal
          05 May 2011
          Article
          10.1088/2041-8205/735/1/L2
          1105.0990

          http://arxiv.org/licenses/nonexclusive-distrib/1.0/

          Custom metadata
          Accepted for publication in ApJL -- 5 pages, 2 figures
          astro-ph.SR astro-ph.HE

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