DISCOVERY OF A YOUNG L DWARF BINARY, SDSS J224953.47+004404.6AB
- Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States)
We report discovery of a young 0.''32 L dwarf binary, SDSS J2249+0044AB, found as the result of a Keck laser guide star adaptive optics imaging survey of young field brown dwarfs. Weak K I, Na I, and FeH features as well as strong VO absorption in the integrated-light J-band spectrum indicate a low surface gravity and hence young age for the system. From spatially resolved K-band spectra we determine spectral types of L3 {+-} 0.5 and L5 {+-} 1 for components A and B, respectively. SDSS J2249+0044A is spectrally very similar to G196-3B, an L3 companion to a young M2.5 field dwarf. Thus, we adopt 100 Myr (the age estimate of the G196-3 system) as the age of SDSS J2249+0044AB, but ages of 12-790 Myr are possible. By comparing our photometry to the absolute magnitudes of G196-3B, we estimate a distance to SDSS J2249+0044AB of 54 {+-} 16 pc and infer a projected separation of 17 {+-} 5 AU for the binary. Comparison of the luminosities to evolutionary models at an age of 100 Myr yields masses of 0.029 {+-} 0.006 and 0.022{sup +0.006}{sub -0.009} M{sub sun} for SDSS J2249+0044A and B, respectively. Over the possible ages of the system (12-790 Myr), the mass of SDSS J2249+0044A could range from 0.011 to 0.070 M{sub sun} and the mass of SDSS J2249+0044B could range from 0.009 to 0.065 M{sub sun}. Evolutionary models predict that either component could be burning deuterium, which could result in a mass ratio as low as 0.4, or alternatively, a reversal in the luminosities of the binary. We find a likely proper motion companion, GSC 00568-01752, which lies 48.''9 away (a projected separation of 2600 AU) and has Sloan Digital Sky Survey and Two Micron All Sky Survey colors consistent with an early M dwarf. We calculate a photometric distance to GSC 00568-01752 of 53 {+-} 15 pc, in good agreement with our distance estimate for SDSS J2249+0044AB. The space motion of SDSS J2249+0044AB shows no obvious coincidence with known young moving groups, though radial velocity and parallax measurements are necessary to refine our analysis. The unusually red near-IR colors, young age, and low masses of the binary make it an important template for studying planetary-mass objects found by direct imaging surveys.
- OSTI ID:
- 21448714
- Journal Information:
- Astrophysical Journal, Vol. 715, Issue 1; Other Information: DOI: 10.1088/0004-637X/715/1/561; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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