1995A&A...294..835C

We have investigated the properties of the OMC-2 and OMC-3 cores in the Orion giant molecular cloud using high spatial and spectral resolution observations of several transitions of the ¹³CO, C¹⁸O, C³²S and C³⁴S molecules taken with the SEST telescope. The OMC-2 core consists of one clump (22M_☉) with a radius of 0.11pc surrounded by a cluster of 11 discrete infrared sources. The H₂ column density and volume density in the center of this clump are 2x10²²cm^–2 and 9x10⁵cm^–3 respectively. From a comparison between physical parameters derived from C¹⁸O and C³²S observations we conclude that the molecular envelope around the core has been completely removed by these sources and that only the very dense gas is left. OMC-3 shows a more complex elongated structure in C¹⁸O and CS than OMC-2. The C³²S and C³⁴S maps show that the denser region can be separated into at least three sub-cores of roughly equal sizes (radius≃0.13pc), with n(H₂)=6x10⁵cm^–3, and a mass of 10M_☉(from C³²S). The very different masses obtained for the central core from C¹⁸O and C³²S (55 and 12M_☉respectively) indicate that a massive envelope is still present around the very dense sub-cores. We report the first detection of several molecular outflows in OMC-3. The presence of an IRAS source and the first detection of these outflows confirm that star formation is going on in OMC-3. Based on the different physical properties of these regions compared with OMC-1, OMC-2 appears to be in an intermediate evolutionary stage between OMC-1 and OMC-3.