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dc.contributor.authorAntonova, A.
dc.contributor.authorDoyle, J. G.
dc.contributor.authorHallinan, G.
dc.contributor.authorBourke, S.
dc.contributor.authorGolden, A.
dc.date.accessioned2018-09-20T15:59:53Z
dc.date.available2018-09-20T15:59:53Z
dc.date.issued2008-06-04
dc.identifier.citationAntonova, A. Doyle, J. G.; Hallinan, G.; Bourke, S.; Golden, A. (2008). A mini-survey of ultracool dwarfs at 4.9 ghz. Astronomy & Astrophysics 487 (1), 317-322
dc.identifier.issn0004-6361,1432-0746
dc.identifier.urihttp://hdl.handle.net/10379/10262
dc.description.abstractContext. 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 mu Jy. The light-curve of 2MASS J07464256+2000321, is dominated towards the end of the observation by a very bright, approximate to 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 approximate to 160 mu Jy in the first hour of observation rising to approximate to 400 mu 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.
dc.publisherEDP Sciences
dc.relation.ispartofAstronomy & Astrophysics
dc.subjectstars : low-mass, brown dwarfs
dc.subjectradio continuum : stars
dc.subjectradiation mechanisms : general
dc.subjectmasers
dc.subjectelectron-cyclotron maser
dc.subjectall-sky survey
dc.subjectbinary l-dwarf
dc.subjectradio-emission
dc.subjectbrown dwarf
dc.subjectt-dwarfs
dc.subjectrotational modulation
dc.subjectinfrared photometry
dc.subjectx-ray
dc.subjectdiscovery
dc.titleA mini-survey of ultracool dwarfs at 4.9 ghz
dc.typeArticle
dc.identifier.doi10.1051/0004-6361:20079275
dc.local.publishedsourcehttps://www.aanda.org/articles/aa/pdf/2008/31/aa9275-07.pdf
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