2003ApJ...592.1186B

We present the discovery of the first L-type subdwarf, 2MASS J05325346+8246465. This object exhibits enhanced collision-induced H₂absorption, resulting in blue near-infrared (NIR) colors (J-K_s=0.26±0.16). In addition, strong hydride bands in the red optical and NIR, weak TiO absorption, and an optical/J-band spectral morphology similar to the L7 DENIS 0205-1159AB imply a cool, metal-deficient atmosphere. We find that 2MASS 0532+8246 has both a high proper motion, µ=2".60±0".15yr^–1, and a substantial radial velocity, v_rad=-195±11 km/s, and its probable proximity to the Sun (d=10-30 pc) is consistent with halo membership. Comparison to subsolar-metallicity evolutionary models strongly suggests that 2MASS 0532+8246 is substellar, with a mass of 0.077≲M≲0.085M_☉for ages 10-15 Gyr and metallicities Z=0.1-0.01Z_☉. The discovery of this object clearly indicates that star formation occurred below the hydrogen burning mass limit at early times, consistent with prior results indicating a flat or slightly rising mass function for the lowest mass stellar subdwarfs. Furthermore, 2MASS 0532+8246 serves as a prototype for a new spectral class of subdwarfs, additional examples of which could be found in NIR proper-motion surveys.