Issue |
A&A
Volume 446, Number 2, February I 2006
|
|
---|---|---|
Page(s) | 485 - 500 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20053493 | |
Published online | 13 January 2006 |
Seventeen new very low-mass members in Taurus
The brown dwarf deficit revisited
1
Laboratoire d'Astrophysique de Grenoble, BP 53, 38041 Grenoble, France e-mail: sylvain.guieu@obs.ujf-grenoble.fr
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: ege@iac.es
6
University of Central Florida, Department of Physics, PO Box 162385, Orlando, FL 32816-2385, USA
Received:
23
May
2005
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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