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

A. Antonova, J. G. Doyle, G. Hallinan, A. Golden, C. Koen

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

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 κJy 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.

Original languageEnglish (US)
Pages (from-to)257-260
Number of pages4
JournalAstronomy and Astrophysics
Volume472
Issue number1
DOIs
StatePublished - Sep 2007
Externally publishedYes

Fingerprint

radioactivity
radio
radio emission
Very Large Array (VLA)
electron
masers
polar regions
inclination
cyclotrons
inspection
modulation
causes
detection
electrons

Keywords

  • Masers
  • Radiation mechanisms: general
  • Radio continuum: stars
  • Stars: activity
  • Stars: atmospheres
  • Stars: low-mass, brown dwarfs

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Antonova, A., Doyle, J. G., Hallinan, G., Golden, A., & Koen, C. (2007). Sporadic long-term variability in radio activity from a brown dwarf. Astronomy and Astrophysics, 472(1), 257-260. https://doi.org/10.1051/0004-6361:20077231

Sporadic long-term variability in radio activity from a brown dwarf. / Antonova, A.; Doyle, J. G.; Hallinan, G.; Golden, A.; Koen, C.

In: Astronomy and Astrophysics, Vol. 472, No. 1, 09.2007, p. 257-260.

Research output: Contribution to journalArticle

Antonova, A, Doyle, JG, Hallinan, G, Golden, A & Koen, C 2007, 'Sporadic long-term variability in radio activity from a brown dwarf', Astronomy and Astrophysics, vol. 472, no. 1, pp. 257-260. https://doi.org/10.1051/0004-6361:20077231
Antonova, A. ; Doyle, J. G. ; Hallinan, G. ; Golden, A. ; Koen, C. / Sporadic long-term variability in radio activity from a brown dwarf. In: Astronomy and Astrophysics. 2007 ; Vol. 472, No. 1. pp. 257-260.
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AB - 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 κJy 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.

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