astro-ph/0509317 [abs, ps, pdf, other] :

Title: 17 new very low-mass members in Taurus. The brown dwarf deficit revisited

Authors: S. Guieu (1), C Dougados (1), J.L Monin (1 and 2), E Magnier (3 and 4), E.L Martin (5 and 6) ((1) Laboratoire d'Astrophysique de Grenoble, (2) Institut Universitaire de France, (3) Canada-France-Hawaii Telescope Corporation, (4) University of Hawaii, Institute of Astronomy, (5) Instituto de Astrofisica de Canarias, (5) University of Central Florida, Department of Physics)

Comments: 20 pages, 15 figures

Recent studies of the substellar population in the Taurus cloud have revealed a deficit of brown dwarfs (BD) compared to the Trapezium cluster population (Briceno et al 1998; Luhman 2000; Luhman et al 2003a; Luhman 2004). However, these works have concentrated on the highest stellar density regions of the Taurus cloud. We have performed a large scale optical survey of this region, covering a total area of 30 deg^2, and encompassing the densest part of the cloud as well as their surroundings, down to a mass detection limits of 15 Jupiter Masses (MJ). In this paper, we present the optical spectroscopic follow-up observations of 97 photometrically selected potential new low-mass Taurus members, of which 27 are strong late-M (SpT < M4V) candidates. These observations reveal 5 new very low mass (VLM) Taurus members and 12 new BDs. Combining our observations with previously published results, we derive an updated substellar to stellar ratio in Taurus of Rss =0.23 +/- 0.05. This ratio now appears consistent with the value previously derived in the Trapezium cluster under similar assumptions of 0.26 +/- 0.04. We find strong indication that the relative numbers of BDs with respect to stars is decreased by a factor 2 in the central regions of the aggregates with respect to the more distributed population. Our findings are best explained in the context of the embryo-ejection model where brown dwarfs originate from dynamical interactions in small N unstable multiple systems.

http://arxiv.org/abs/astro-ph/0509317