ANALYSIS OF A COLD CLOUD FRAGMENT

We present CO and CS data of the recently discovered protostar candida te HH24 MMS in the Orion region for which submm/mm continuum observati ons of the dust yielded an angular size of almost-equal-to 15'', a tem perature of about 10K and gave evidence for gravitational instability. The new molecular line data indicate that the source is a cold spot i n an extended molecular cloud because the CO line temperature is highe r than the color temperature of the dust. In contrast to its appearanc e in the dust continuum, the source is not prominent in (CO)-O-18 nor in CS suggesting that the molecules are partially frozen out. There is no indication of a strong outflow in CO. Mass estimates from (CO)-O-1 8 are roughly a hundred times lower than from the mm/submm dust emissi on, The large discrepancy is probably a combined effect of molecular u nder-abundance and an enhanced absorption coefficient of the dust at 1 mm. Furthermore, we calculate theoretical profiles of CO and CS for a cloud core like HH24 MMS in order to identify observable spectral sign atures for collapse. We find that the most promising clue will come fr om CS lines observed with a resolution that is a factor 3 higher than the present data. Such transitions are expected to show an absorption feature that shifts to progressively larger velocities with increasing j-number. The present observations of (CO)-O-18 and CS are in accord with this model.