A mini-survey of ultracool dwarfs at 4.9 GHz

A. Antonova, J. G. Doyle, G. Hallinan, S. Bourke, A. Golden

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Context. A selection of ultracool dwarfs are known to be radio active, with both gyrosynchrotron emission and the electron cyclotron maser instability being given as likely emission mechanisms.Aims. We explore whether ultracool dwarfs previously undetected at 8.5 GHz may be detectable at a lower frequency.Methods. We select a sample of fast rotating ultracool dwarfs with no detectable radio activity at 8.5 GHz, observing each of them at 4.9 GHz.Results. From the 8 dwarfs in our sample, we detect emission from 2MASS J07464256+2000321, with a mean flux level of 286 24 Jy. The light-curve of 2MASS J07464256+2000321, is dominated towards the end of the observation by a very bright, 100% left circularly polarized burst during which the flux reached 2.4 mJy. The burst was preceded by a raise in the level of activity, with the average flux being 160 Jy in the first hour of observation rising to 400 Jy in the 40 min before the burst. During both periods, there is significant variability.Conclusions. The detection of 100% circular polarization in the emission at 4.9 GHz points towards the electron cyclotron maser as the emission mechanism. However, the observations at 4.9 GHz and 8.5 GHz were not simultaneous, thus the actual fraction of dwarfs capable of producing radio emission, as well as the fraction of those that show periodic pulsations is still unclear, as indeed are the relative roles played by the electron cyclotron maser instability versus gyrosynchrotron emission, therefore we cannot assert if the previous non-detection at 8.5 GHz was due to a cut-off in emission between 4.9 and 8.4 GHz, or due to long term variability.

Original languageEnglish (US)
Pages (from-to)317-322
Number of pages6
JournalAstronomy and Astrophysics
Volume487
Issue number1
DOIs
StatePublished - Aug 2008
Externally publishedYes

Fingerprint

masers
cyclotrons
bursts
electron
radio
electrons
radio emission
circular polarization
radioactivity
light curve
cut-off
polarization
low frequencies

Keywords

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

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Antonova, A., Doyle, J. G., Hallinan, G., Bourke, S., & Golden, A. (2008). A mini-survey of ultracool dwarfs at 4.9 GHz. Astronomy and Astrophysics, 487(1), 317-322. https://doi.org/10.1051/0004-6361:20079275

A mini-survey of ultracool dwarfs at 4.9 GHz. / Antonova, A.; Doyle, J. G.; Hallinan, G.; Bourke, S.; Golden, A.

In: Astronomy and Astrophysics, Vol. 487, No. 1, 08.2008, p. 317-322.

Research output: Contribution to journalArticle

Antonova, A, Doyle, JG, Hallinan, G, Bourke, S & Golden, A 2008, 'A mini-survey of ultracool dwarfs at 4.9 GHz', Astronomy and Astrophysics, vol. 487, no. 1, pp. 317-322. https://doi.org/10.1051/0004-6361:20079275
Antonova A, Doyle JG, Hallinan G, Bourke S, Golden A. A mini-survey of ultracool dwarfs at 4.9 GHz. Astronomy and Astrophysics. 2008 Aug;487(1):317-322. https://doi.org/10.1051/0004-6361:20079275
Antonova, A. ; Doyle, J. G. ; Hallinan, G. ; Bourke, S. ; Golden, A. / A mini-survey of ultracool dwarfs at 4.9 GHz. In: Astronomy and Astrophysics. 2008 ; Vol. 487, No. 1. pp. 317-322.
@article{5f5e48421b1f46ac96fac277aab74c57,
title = "A mini-survey of ultracool dwarfs at 4.9 GHz",
abstract = "Context. A selection of ultracool dwarfs are known to be radio active, with both gyrosynchrotron emission and the electron cyclotron maser instability being given as likely emission mechanisms.Aims. We explore whether ultracool dwarfs previously undetected at 8.5 GHz may be detectable at a lower frequency.Methods. We select a sample of fast rotating ultracool dwarfs with no detectable radio activity at 8.5 GHz, observing each of them at 4.9 GHz.Results. From the 8 dwarfs in our sample, we detect emission from 2MASS J07464256+2000321, with a mean flux level of 286 24 Jy. The light-curve of 2MASS J07464256+2000321, is dominated towards the end of the observation by a very bright, 100{\%} left circularly polarized burst during which the flux reached 2.4 mJy. The burst was preceded by a raise in the level of activity, with the average flux being 160 Jy in the first hour of observation rising to 400 Jy in the 40 min before the burst. During both periods, there is significant variability.Conclusions. The detection of 100{\%} circular polarization in the emission at 4.9 GHz points towards the electron cyclotron maser as the emission mechanism. However, the observations at 4.9 GHz and 8.5 GHz were not simultaneous, thus the actual fraction of dwarfs capable of producing radio emission, as well as the fraction of those that show periodic pulsations is still unclear, as indeed are the relative roles played by the electron cyclotron maser instability versus gyrosynchrotron emission, therefore we cannot assert if the previous non-detection at 8.5 GHz was due to a cut-off in emission between 4.9 and 8.4 GHz, or due to long term variability.",
keywords = "Masers, Radiation mechanisms: general, Radio continuum: stars, Stars: low-mass, brown dwarfs",
author = "A. Antonova and Doyle, {J. G.} and G. Hallinan and S. Bourke and A. Golden",
year = "2008",
month = "8",
doi = "10.1051/0004-6361:20079275",
language = "English (US)",
volume = "487",
pages = "317--322",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",
number = "1",

}

TY - JOUR

T1 - A mini-survey of ultracool dwarfs at 4.9 GHz

AU - Antonova, A.

AU - Doyle, J. G.

AU - Hallinan, G.

AU - Bourke, S.

AU - Golden, A.

PY - 2008/8

Y1 - 2008/8

N2 - Context. A selection of ultracool dwarfs are known to be radio active, with both gyrosynchrotron emission and the electron cyclotron maser instability being given as likely emission mechanisms.Aims. We explore whether ultracool dwarfs previously undetected at 8.5 GHz may be detectable at a lower frequency.Methods. We select a sample of fast rotating ultracool dwarfs with no detectable radio activity at 8.5 GHz, observing each of them at 4.9 GHz.Results. From the 8 dwarfs in our sample, we detect emission from 2MASS J07464256+2000321, with a mean flux level of 286 24 Jy. The light-curve of 2MASS J07464256+2000321, is dominated towards the end of the observation by a very bright, 100% left circularly polarized burst during which the flux reached 2.4 mJy. The burst was preceded by a raise in the level of activity, with the average flux being 160 Jy in the first hour of observation rising to 400 Jy in the 40 min before the burst. During both periods, there is significant variability.Conclusions. The detection of 100% circular polarization in the emission at 4.9 GHz points towards the electron cyclotron maser as the emission mechanism. However, the observations at 4.9 GHz and 8.5 GHz were not simultaneous, thus the actual fraction of dwarfs capable of producing radio emission, as well as the fraction of those that show periodic pulsations is still unclear, as indeed are the relative roles played by the electron cyclotron maser instability versus gyrosynchrotron emission, therefore we cannot assert if the previous non-detection at 8.5 GHz was due to a cut-off in emission between 4.9 and 8.4 GHz, or due to long term variability.

AB - Context. A selection of ultracool dwarfs are known to be radio active, with both gyrosynchrotron emission and the electron cyclotron maser instability being given as likely emission mechanisms.Aims. We explore whether ultracool dwarfs previously undetected at 8.5 GHz may be detectable at a lower frequency.Methods. We select a sample of fast rotating ultracool dwarfs with no detectable radio activity at 8.5 GHz, observing each of them at 4.9 GHz.Results. From the 8 dwarfs in our sample, we detect emission from 2MASS J07464256+2000321, with a mean flux level of 286 24 Jy. The light-curve of 2MASS J07464256+2000321, is dominated towards the end of the observation by a very bright, 100% left circularly polarized burst during which the flux reached 2.4 mJy. The burst was preceded by a raise in the level of activity, with the average flux being 160 Jy in the first hour of observation rising to 400 Jy in the 40 min before the burst. During both periods, there is significant variability.Conclusions. The detection of 100% circular polarization in the emission at 4.9 GHz points towards the electron cyclotron maser as the emission mechanism. However, the observations at 4.9 GHz and 8.5 GHz were not simultaneous, thus the actual fraction of dwarfs capable of producing radio emission, as well as the fraction of those that show periodic pulsations is still unclear, as indeed are the relative roles played by the electron cyclotron maser instability versus gyrosynchrotron emission, therefore we cannot assert if the previous non-detection at 8.5 GHz was due to a cut-off in emission between 4.9 and 8.4 GHz, or due to long term variability.

KW - Masers

KW - Radiation mechanisms: general

KW - Radio continuum: stars

KW - Stars: low-mass, brown dwarfs

UR - http://www.scopus.com/inward/record.url?scp=48249150801&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=48249150801&partnerID=8YFLogxK

U2 - 10.1051/0004-6361:20079275

DO - 10.1051/0004-6361:20079275

M3 - Article

AN - SCOPUS:48249150801

VL - 487

SP - 317

EP - 322

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 0004-6361

IS - 1

ER -