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Sporadic long-term variability in radio activity from a brown dwarf

Antonova, A. and Doyle, J. G. and Hallinan, G. and Golden, A. and Koen, C. (2007) Sporadic long-term variability in radio activity from a brown dwarf. Astronomy and Astrophysics, 472 (1). pp. 257-260. ISSN 0004-6361.

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Context. Radio activity has been observed in a large variety of stellar objects, including in the last few years, ultra-cool dwarfs. Aims. To explore the extent of long-term radio activity in ultra-cool dwarfs. Methods. We use data taken over an extended period of 9 hr from the Very Large Array of the source 2MASS J05233822-1403022 in September 2006, plus data taken in 2004. Results. The observation taken in September 2006 failed to detect any radio activity at 8.46 GHz. A closer inspection of earlier data reveals that the source varied from a null detection on 3 May 2004, to ≈95 µJy on 17 May 2004, to 230 µJy on 18 June 2004. The lack of detection in September 2006 suggests at least a factor of ten flux variability at 8.46 GHz. Three short photometric runs did not reveal any optical variability. Conclusions. In addition to the observed pulsing nature of the radio flux from another ultra-cool source, the present observations suggests that ultra-cool dwarfs may not just be pulsing but can also display long-term sporadic variability in their levels of quiescent radio emission. The lack of optical photometric variability suggests an absence of large-scale spots at the time of the latest VLA observations, although small very high latitude spots combined with a low inclination could cause very low amplitude rotational modulation which may not be measurable. We discuss this large variability in the radio emission within the context of both gyrosynchrotron emission and the electron-cyclotron maser, favoring the latter mechanism.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper DOIArticle
Hallinan, G.0000-0002-7083-4049
Golden, A.0000-0002-8599-2031
Additional Information:© 2007 ESO. Article published by EDP Sciences. Received 2 February 2007; Accepted 11 June 2007. Armagh Observatory is grant-aided by the N. Ireland Dept. of Culture, Arts & Leisure. The authors thank Stephen Bourke for his help with IRAF and Kathlin Olah for advice on spot modelling. We also gratefully acknowledge the support of the HEA funded Cosmogrid project and Enterprise Ireland under the grant award SC/2001/0322, plus PPARC for a visitor grant.
Funding AgencyGrant Number
Northern Ireland Department of Culture, Arts and Leisure (DCAL)UNSPECIFIED
HEA Funded Cosmogrid ProjectUNSPECIFIED
Enterprise IrelandSC/2001/0322
Particle Physics and Astronomy Research Council (PPARC)UNSPECIFIED
Subject Keywords:stars: activity – stars: atmospheres – stars: low-mass, brown dwarfs – radio continuum: stars – masers – radiation mechanisms: general
Issue or Number:1
Record Number:CaltechAUTHORS:20140204-140139750
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Official Citation:Sporadic long-term variability in radio activity from a brown dwarf A. Antonova, J. G. Doyle, G. Hallinan, A. Golden, C. Koen A&A 472 (1) 257-260 (2007) DOI: 10.1051/0004-6361:20077231
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43655
Deposited By: Tony Diaz
Deposited On:25 Feb 2014 17:44
Last Modified:09 Mar 2020 13:18

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