Title

Seventeen New Very Low-Mass Members In Taurus The Brown Dwarf Deficit Revisited

Keywords

Stars: late-type; Stars: low-mass, brown dwarfs; Stars: luminosity function, mass function; Stars: pre-main sequence

Abstract

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 ≃28 deg 2, and encompassing the densest parts of the cloud as well as their surroundings, down to a mass detection limit of 15 M J. 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 (SpT ≥ M4V) candidates. Our spectroscopic survey is 87% complete down to i′ = 20 for spectral types later than M4V, which corresponds to a mass completeness limit of 30 M J for ages ≤10 Myr and Av ≤ 4. 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 Hα 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 R SS = 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 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. © ESO 2006.

Publication Date

2-1-2006

Publication Title

Astronomy and Astrophysics

Volume

446

Issue

2

Number of Pages

485-500

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1051/0004-6361:20053493

Socpus ID

31544477142 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/31544477142

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