2mass-allsky

The First Substellar Subdwarf? Discovery of a Metal-poor L Dwarf with Halo Kinematics

August 2003 • 2003ApJ...592.1186B

Authors • Burgasser, Adam J. • Kirkpatrick, J. Davy • Burrows, Adam • Liebert, James • Reid, I. Neill • Gizis, John E. • McGovern, Mark R. • Prato, L. • McLean, Ian S.

Abstract • We present the discovery of the first L-type subdwarf, 2MASS J05325346+8246465. This object exhibits enhanced collision-induced H2 absorption, resulting in blue near-infrared (NIR) colors (J-Ks=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"+/-0.15"yr-1, and a substantial radial velocity, vrad=-195+/-11 km s-1, 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<~0.085Msolar for ages 10-15 Gyr and metallicities Z=0.1-0.01Zsolar. 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.

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Davy Kirkpatrick

Senior Scientist