Parallax and Luminosity Measurements of an L Subdwarf

• Published in: The Astrophysical journal 2008-01, Vol.672 (2), p.1159-1166
• Main Authors: Burgasser, Adam J, Vrba, Frederick J, Lépine, Sébastien, Munn, Jeffrey A, Luginbuhl, Christian B, Henden, Arne A, Guetter, Harry H, Canzian, Blaise C
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/523810

We present the first parallax and luminosity measurements for an L subdwarf, the sdL7 2MASS J05325346+8246465. Observations conducted over 3 years by the USNO Infrared astrometry program yield an astrometric distance of 26.7 plus or minus 1.2 pc and a proper motion of 2.6241" plus or minus 0.0018" yr super(-1). Combined with broadband spectral and photometric measurements, we determine a luminosity of log L sub(bol)/L [unk] = 4.24 plus or minus 0.06 and T [unk] = 1730 plus or minus 90 K (the latter assuming an age of 5-10 Gyr), comparable to mid-type L field dwarfs. Comparison of the luminosity of 2MASS J05325346+8246465 to theoretical evolutionary models indicates that its mass is just below the sustained hydrogen-burning limit, and is therefore a brown dwarf. Its kinematics indicate a similar to 110 Myr, retrograde Galactic orbit that is both eccentric (3 kpc [unk] R [unk] 8.5 kpc) and extends well away from the plane ( Delta Z = plus or minus 2 kpc), consistent with membership in the inner halo population. The relatively bright J-band magnitude of 2MASS J05325346+8246465 implies significantly reduced opacity in the 1.2 mu m region, consistent with inhibited condensate formation as previously proposed. Its as yet unknown subsolar metallicity remains the primary limitation in constraining its mass; determination of both parameters would provide a powerful test of interior and evolutionary models for low-mass stars and brown dwarfs.