EVOLUTIONARY STATUS OF BRIGHTEST AND YOUNGEST SOURCE IN THE ORION MOLECULAR CLOUD –3 REGION

The brightest continuum source in the Orion Molecular Cloud-3 region (OMC-3), MMS 6, was observed with the Very Large Array (VLA), the Nobeyama Millimeter Array (NMA), and the Submillimeter Array (SMA). Our data were supplemented by near- to mid-infrared archival data taken by Spitzer Space Telescope. The compact continuum source, MMS 6-main, was detected with an H_2 mass of 3.0 Msun with a size of 510 AU. Despite its compact and well condensed appearance, neither clear CO outflow, radio jet, nor infrared sources (at a wave-length shorter than 8 um) were detected at MMS 6-main even with the present high-spatial resolution and high-sensitivity observations. The derived H_2 column density, 2.6x10^25 cm^-2, corresponds to a visual extinction of A_v~15000 mag., and the derived number density is at least two orders of magnitude higher than for the other OMC-2/3 continuum sources. The volume density profile of the source was estimated to have a power-law index of 2 or steeper down to a radius of ~450 AU. The time scale to form a protostar at the center or the time scale elapsed after its formation is estimated to be 830 to 7600 yr. This is much shorter than the typical lifetime of the Class 0/I protostars, which is ~10^(4-5) yr, suggesting that MMS 6-main is probably in either the earliest stage of the proto-stellar core or in the latest stage of the pre-stellar phase.
34 pages, 7 figures, accepted to ApJ