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Description
We have performed a large scale optical survey of the Taurus cloud, covering a total area of 28deg^2^, and encompassing the densest parts of the cloud as well as their surroundings, down to a mass detection limit of 15 Jupiter masses. 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 SpType<M4V candidates. 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 brown dwarfs. 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 brown dwarfs 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.
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