The First Substellar Subdwarf? Discovery of a Metal-poor L Dwarf with Halo Kinematics
We present the discovery of the first L-type subdwarf, 2MASSJ05325346+8246465. This object exhibits enhanced collision-inducedH2 absorption, resulting in blue near-infrared (NIR) colors(J-Ks=0.26+/-0.16). In addition, strong hydride bands in thered optical and NIR, weak TiO absorption, and an optical/J-band spectralmorphology similar to the L7 DENIS 0205-1159AB imply a cool,metal-deficient atmosphere. We find that 2MASS 0532+8246 has both a highproper motion, ?=2.60"+/-0.15"yr-1, and a substantialradial velocity, vrad=-195+/-11 km s-1, and itsprobable proximity to the Sun (d=10-30 pc) is consistent with halomembership. Comparison to subsolar-metallicity evolutionary modelsstrongly suggests that 2MASS 0532+8246 is substellar, with a mass of0.077<~M<~0.085Msolar for ages 10-15 Gyr andmetallicities Z=0.1-0.01Zsolar. The discovery of this objectclearly indicates that star formation occurred below the hydrogenburning mass limit at early times, consistent with prior resultsindicating a flat or slightly rising mass function for the lowest massstellar subdwarfs. Furthermore, 2MASS 0532+8246 serves as a prototypefor a new spectral class of subdwarfs, additional examples of whichcould be found in NIR proper-motion surveys.
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