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

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

2003-04-09

arxiv.org/abs/astro-ph/0304174v1

Astrophys.J. 592 (2003) 1186-1192

Astronomy and Astrophysics

Astrophysics

9 pages, 3 figures, accepted to ApJ

Scientific paper

10.1086/375813

We present the discovery of the first L-type subdwarf, 2MASS J05325346+8246465. This object exhibits enhanced collision-induced H$_2$ absorption, resulting in blue NIR colors ($J-K_s = 0.26{\pm}0.16$). 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, $\mu$ = 2$\farcs60\pm0\farcs$15 yr$^{-1}$, and a substantial radial velocity, $v_{rad} = -195{\pm}11$ 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 $\lesssim$ M $\lesssim$ 0.085 M$_{\sun}$ for ages 10--15 Gyr and metallicities $Z = 0.1-0.01$ $Z_{\sun}$. 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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