Millimeter- and Submillimeter-Wave Observations of the OMC-2/3 Region. I. Dispersing and Rotating Core around the Intermediate-Mass Protostar MMS 7*

摘要

We report the results of H13CO+ (1-0), CO (1-0), and 3.3 mm dust continuum observations toward MMS 7, one of the strongest millimeter-wave sources in OMC-3, with the Nobeyama Millimeter Array (NMA) and the Nobeyama 45 m telescope. With the NMA, we detected centrally condensed 3.3 mm dust continuum emission, which coincides with the mid-infrared (MIR) source and the free-free jet. Our H13CO+ observations revealed a disklike envelope around MMS 7, whose size and mass are 0.15 × 0.11 pc and 5.1 M☉, respectively. The outer portion of the disklike envelope has a fan-shaped structure, which delineates the rim of the observed CO outflow. The position-velocity diagrams in the H13CO+ (1-0) emission show that the velocity field in the disklike envelope is composed of a dispersing gas motion and a possible rigid-like rotation. The mass-dispersing rate is estimated to be 3.4 × 10-5 M☉ yr-1, which implies that MMS 7 has an ability to disperse ~10 M☉ during the protostellar evolutional time. The specific angular momentum in the disklike envelope is nearly 2 orders of magnitude larger than that in low-mass cores. The turnover point of the power law of the angular momentum distribution in the disklike envelope (≤0.007 pc), which is likely to be related to the outer radius of the central mass accretion, is similar in size to the 3.3 mm dust condensation. We propose that MMS 7 is in the last stage of the main accretion phase and that a substantial portion of the outer gas has already been dispersed, while mass accretion may still be ongoing at the innermost region, traced by the dusty condensation.