1994A&A...287..947K

We present CO and CS data of the recently discovered protostar candidate HH24 MMS in the Orion region for which submm/mm continuum observations of the dust yielded an angular size of ≃15", a temperature of about 10K and gave evidence for gravitational instability. The new molecular line data indicate that the source is a cold spot in an extended molecular cloud because the CO line temperature is higher than the color temperature of the dust. In contrast to its appearance in the dust continuum, the source is not prominent in C¹⁸O nor in CS suggesting that the molecules are partially frozen out. There is no indication of a strong outflow in CO. Mass estimates from C¹⁸O are roughly a hundred times lower than from the mm/submm dust emission. The large discrepancy is probably a combined effect of molecular underabundance and an enhanced absorption coefficient of the dust at 1mm. Furthermore, we calculate theoretical profiles of CO and CS for a cloud core like HH24 MMS in order to identify observable spectral signatures for collapse. We find that the most promising clue will come from 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 C¹⁸O and CS are in accord with this model.