Peer-Reviewed Journal Details
Mandatory Fields
Harding L.K., Hallinan G., Boyle R. P., Golden A., Singh N., Sheehan B., Zavala R., Butler R. F.
The Astrophysical Journal
Periodic Optical Variability of Radio Detected Ultracool Dwarfs
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22 pages
A fraction of very low mass stars and brown dwarfs are known to be radioactive, in some cases producing periodic pulses. Extensive studies of two suchobjects have also revealed optical periodic variability and the nature of thisvariability remains unclear. Here we report on multi-epoch optical photometricmonitoring of six radio detected dwarfs, spanning the $\sim$M8 - L3.5 spectralrange, conducted to investigate the ubiquity of periodic optical variability inradio detected ultracool dwarfs. This survey is the most sensitive ground-basedstudy carried out to date in search of periodic optical variability fromlate-type dwarfs, where we obtained 250 hours of monitoring, deliveringphotometric precision as low as $\sim$0.15\%. Five of the six targets exhibitclear periodicity, in all cases likely associated with the rotation period ofthe dwarf, with a marginal detection found for the sixth. Our data points to alikely association between radio and optical periodic variability inlate-M/early-L dwarfs, although the underlying physical cause of thiscorrelation remains unclear. In one case, we have multiple epochs of monitoringof the archetype of pulsing radio dwarfs, the M9 TVLM 513-46546, spanning aperiod of 5 years, which is sufficiently stable in phase to allow us toestablish a period of 1.95958 $\pm$ 0.00005 hours. This phase stability may beassociated with a large-scale stable magnetic field, further strengthening thecorrelation between radio activity and periodic optical variability. Finally,we find a tentative spin-orbit alignment of one component of the very low massbinary LP 349-25.
Grant Details
NUI Travelling Studentship in the Sciences (2010)
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