PROTO-BROWN DWARFS .2. RESULTS IN THE OPHIUCHUS AND TAURUS MOLECULAR CLOUDS

We expand our proto-brown dwarf search to include two nearby star-forming regions in the Ophiuchus and Taurus molecular clouds. In both molecular line and continuum searches in the Ophiuchus B and Barnard 18 (in Taurus) star-forming regions, we find no clear-cut evidence of any proto-brown dwarfs. This lack of proto-brown dwarfs is surprising; even if the initial mass function (IMF) (given by dN/dM proportional to M(-alpha)) were flat (alpha = 1), we would expect to have found similar to 10 objects. We do find, however, a few candidate objects near our detection limit (similar to 0.02 M.) which deserve further scrutiny. We find 21 gravitationally bound clumps distributed in mass with a spectral index alpha = 1.1 +/- 0.2. However, there are fewer low-mass clumps (less than or similar to 0.1 M.) than would be expected from extrapolation of any reasonable mass function, including the well-known giant molecular cloud dump mass spectrum. If the IMF follows the clump mass spectrum below 0.08 M., as it does at higher masses, our results in Oph B imply that, unless some undetermined process causes the production of many more low-mass clumps, the IMF is falling at masses below 0.08 M., even if all our candidate objects turn out to be true proto-brown dwarfs. This work presents evidence that there is a mass range (0.1-0.25 M.) where the molecular cloud clump mass spectrum has the same slope stellar IMF (alpha similar to 1). This is an indication that there is indeed a direct relationship between clump mass and subsequent stellar mass at the scale of a few tenths of a solar mass.