Volume 446, Number 2, February I 2006
|Page(s)||485 - 500|
|Section||Galactic structure, stellar clusters, and populations|
|Published online||13 January 2006|
Seventeen new very low-mass members in Taurus
The brown dwarf deficit revisited
Laboratoire d'Astrophysique de Grenoble, BP 53, 38041 Grenoble, France e-mail: firstname.lastname@example.org
2 Institut Universitaire de France
3 Canada-France-Hawaii Telescope Corporation, PO Box 1597, Kamuela, USA
4 University of Hawaii, Institute of Astronomy, 2680 Woodlawn Dr., Honolulu, HI 96821, USA
5 Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife, Spain e-mail: email@example.com
6 University of Central Florida, Department of Physics, PO Box 162385, Orlando, FL 32816-2385, USA
Accepted: 9 September 2005
Recent studies of the substellar population in the Taurus cloud have revealed a deficit of brown dwarfs compared to the Trapezium cluster population. 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 , and encompassing the densest parts of the cloud as well as their surroundings, down to a mass detection limit of 15 MJ. 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 spectral type () candidates. Our spectroscopic survey is 87% complete down to for spectral types later than M4V, which corresponds to a mass completeness limit of 30 MJ for ages ≤10 Myr and . We derive spectral types, visual absorption and luminosity class estimates and discuss our criteria to assess Taurus membership. These observations reveal 5 new VLM Taurus members and 12 new BDs. Two of the new VLM sources and four of the new substellar members exhibit accretion/outflow signatures similar to higher mass classical T Tauri stars. From levels of emission we derive a fraction of accreting sources of 42% in the substellar Taurus population. Combining our observations with previously published results, we derive an updated substellar to stellar ratio in Taurus of . This ratio now appears consistent with the value previously derived in the Trapezium cluster under similar assumptions of . We find indications 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.
Key words: stars: low-mass, brown dwarfs / stars: late-type / stars: luminosity function, mass function / stars: pre-main sequence
© ESO, 2006
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