THE MAGNETOSPHERE OF THE ULTRACOOL DWARF DENIS 1048-3956

Journal Article · Fri Jul 01 00:00:00 EDT 2011 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/735/1/L2· OSTI ID:21562581

Ravi, V ^[1]; Hallinan, G ^[2]; Hobbs, G ^[3]; Champion, D J ^[4]

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1. Research School of Astronomy and Astrophysics, ANU, Mt. Stromlo Observatory, Weston ACT 2611 (Australia)
2. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
3. CSIRO Astronomy and Space Sciences, Australia Telescope National Facility, P.O. Box 76, Epping NSW 1710 (Australia)
4. Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121, Bonn (Germany)

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 corotation radius, R{sub C} , of the star. Adopting this model, we find R{sub C} between 1.2 R{sub *} and 2.9 R{sub *}, and a non-thermal electron density and magnetic field strength between 10{sup 5} and 10{sup 7.2} cm{sup -3} and between 70 and 260 G, respectively, at R{sub 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.

• OSTI ID: 21562581
• Journal Information: Astrophysical Journal Letters, Vol. 735, Issue 1; Other Information: DOI: 10.1088/2041-8205/735/1/L2; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
DWARF STARS
ELECTRON DENSITY
EMISSION
LUMINOSITY
MAGNETIC FIELDS
MAGNETIC PROPERTIES
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
STARS