The Brown Dwarf Deficit in Taurus: Evidence for a Non-Universal IMF

Abstract

We present the results of a deep, optical/IR wide field imaging survey of selected fields in the nearby (d~ 140 pc) Taurus star-forming region. We report the discovery of 9 new members with spectral types M5.75–M9.5. We derive an Initial Mass Function encompassing 54% of the known members in Taurus. Comparison with dense regions like the Trapezium Cluster in Orion shows that Taurus has produced x2 less brown dwarfs. We suggest that the lower frequency of brown dwarfs in Taurus may result from the low-density star-forming environment, leading to larger minimum Jeans masses.