The First L-type Brown Dwarf in the Pleiades
Abstract
We have obtained low-resolution optical spectra of three faint brown dwarf candidates in the Pleiades open cluster. The objects observed are Roque 12 (I=18.5), Roque 5 (I=19.7) and Roque 25 (I=21.2). The spectrum of Roque 25 does not show the strong TiO bandheads that characterize the optical spectra of M-type stars, but molecular bands of CaH, CrH and VO are clearly present. We classify Roque 25 as an early L-type brown dwarf. Using current theoretical evolutionary tracks we estimate that the transition from M-type to L-type in the Pleiades (age ~ 120 Myr) takes place at Teff ~ 2200 K or M ~ 0.04 Msol. Roque 25 is a benchmark brown dwarf in the Pleiades because it is the first known one that belongs to the L-type class. It provides evidence that the IMF extends down to about 0.035 Msol, and serves as a guide for future deep searches for even less massive young brown dwarfs.
Keywords
Cite
@article{arxiv.astro-ph/9809031,
title = {The First L-type Brown Dwarf in the Pleiades},
author = {E. L. Martin and G. Basri and M. R. Zapatero Osorio and R. Rebolo and R. J. Garcia Lopez},
journal= {arXiv preprint arXiv:astro-ph/9809031},
year = {2009}
}
Comments
18 pages; ApJ Letters (accepted); also available at http://www.iac.es/publicaciones/preprints.html