Parallax and luminosity measurements of an L subdwarf

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 +/- 1.2 pc and a proper motion of 2.624100 '' +/- 0. 001800 '' yr(-1). Combined with broadband spectral and photometric measurements, we determine a luminosity of log L-bol/L-circle dot = 4.24 +/- 0.06 and T-eff = 1730 +/- 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 less than or similar to R less than or similar to 8.5 kpc) and extends well away from the plane (Delta Z = +/- 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.