Astronomy and Astrophysics, volume 446, 485-500 (2006/2-1)
Seventeen new very low-mass members in Taurus. The brown dwarf deficit revisited.
GUIEU S., DOUGADOS C., MONIN J.-L., MAGNIER E. and MARTIN E.L.
Abstract (from CDS):
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 ≃28deg2, and encompassing the densest parts of the cloud as well as their surroundings, down to a mass detection limit of 15MJ. 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 30MJ for ages ≤10Myr 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 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 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.
stars: low-mass, brown dwarfs - stars: late-type - stars: luminosity function, mass function - stars: pre-main sequence
VizieR on-line data:
<Available at CDS (J/A+A/446/485): table3.dat table4.dat table5.dat>
Table 4: [MDM2001] CFHT-BD-Tau NN (Nos 9-21) added.
Paragraph. 4.4 J0442713+2512164 is a misprint for 2MASS J04442713+2512164.
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