Other
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.9602r&link_type=abstract
American Astronomical Society Meeting 210, #96.02; Bulletin of the American Astronomical Society, Vol. 39, p.225
Other
Scientific paper
Emission in Hα is commonly seen among M dwarfs, with the activity levels increasing towards later types, reaching a peak at M7. Beyond spectral type M7, there is a drop off in Hα activity, with a rapid decline seen for the L dwarfs. There exists, however, a small population of late-M, L and T dwarfs that exhibit strong flaring in the Hα emission line. While different explanations have been suggested for these rare displays of strong Hα emission, the mechanism that empowers such flares is still unknown. We discuss here Spitzer IRAC observations of the L5 dwarf 2MASSI J1315309-264951 (2M1315) that has been found to display strong Hα emission. The existing six epochs of spectroscopy suggest that the emission in Hα is not persistent, but shows a long-term variability between a flare value of 100 angs and a quiescent value of 25 angs. We have not detected excess emission in any of the IRAC bands for 2M1315, that would indicate the presence of an accretion disk. The IRAC colors for this brown dwarf are redder by 0.1 mag compared with other L5 dwarfs, and more similar to the late-type L dwarfs. We have measured a proper motion of 0.79"± 0.06"/yr, that corresponds to a tangential velocity of ˜81 km/s, at a distance of ˜22 pc. Evolutionary models indicate lower limits of 3.3 Gyr (Chabrier et al.) or 1.4 Gyr (Burrows et al.) for this magnetically active L dwarf to be a stable hydrogen-burning star. There seem to be no observational differences between this old L dwarf that has Hα emission and the other field L dwarfs without it. We will discuss in this presentation the likely explanations for the unusual Hα activity seen in this brown dwarf.
Gizis John
Riaz Basmah
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