Proto-brown dwarfs. 2: Results in the Ophiuchus and Taurus moleculra clouds

Details Proto-brown dwarfs. 2: Results in the Ophiuchus and Taurus moleculra clouds Proto-brown dwarfs. 2: Results in the Ophiuchus and Taurus moleculra clouds

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...444..270p&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 444, no. 1, p. 270-287

Astronomy and Astrophysics

Astrophysics

13

Brown Dwarf Stars, Clumps, Interstellar Matter, Molecular Clouds, Stellar Mass, Astronomical Maps, Emission Spectra, Mass Spectra, Molecular Spectra, Star Formation

Scientific paper

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 approximately 10 objects. We do find, however, a few candidate objects near our detection limit (approximately 0.02 solar mass) 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 (approximately less than 0.1 solar mass) than would be expected from extrapolation of any reasonable mass function, including the well-known giant molecular cloud clump mass spectrum. If the IMF follows the clump mass spectrum below 0.08 solar mass, 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 solar mass, 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 solar mass) where the molecular cloud clump mass spectrum has the same slope stellar IMF (alpha approximately 1). This is an indication that there is indeed a direct relationship between clump mass and subsequent stellar mass and subsequent stellar mass at the scale of a few tenths of a solar mass.

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