Seventeen new very low-mass members in Taurus - The brown dwarf deficit revisited

    Authors

    S. Guieu; C. Dougados; J. L. Monin; E. Magnier;E. L. Martin

    Comments

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    Abbreviated Journal Title

    Astron. Astrophys.

    Keywords

    stars : low-mass; brown dwarfs; stars : late-type; stars : luminosity; function; mass function; stars : pre-main sequence; SPECTRAL ENERGY-DISTRIBUTIONS; FRANCE-HAWAII-TELESCOPE; ORION NEBULA; CLUSTER; STAR-FORMING REGION; MAIN-SEQUENCE STARS; ALL-SKY SURVEY; INFRARED EXCESSES; IC 348; AURIGA; ACCRETION; Astronomy & Astrophysics

    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 similar or equal to 28 deg2, 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 MJ 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 Ha 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.

    Journal Title

    Astronomy & Astrophysics

    Volume

    446

    Issue/Number

    2

    Publication Date

    1-1-2006

    Document Type

    Article

    Language

    English

    First Page

    485

    Last Page

    500

    WOS Identifier

    WOS:000234651700012

    ISSN

    0004-6361

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