Abstract
Abstract We have observed the young protostellar system NGC 2264 CMM3 in the 1.3 mm and 2.0 mm bands at a resolution of about 0.″1 (70 au) with ALMA. The structures of two distinct components, CMM3A and CMM3B, are resolved in the continuum images of both bands. CMM3A has an elliptical structure extending along the direction almost perpendicular to the known outflow, while CMM3B reveals a round shape. We have fitted two 2D Gaussian components to the elliptical structure of CMM3A and CMM3B and have separated the disk and envelope components for each source. The spectral index α between 2.0 and 0.8 mm is derived to be 2.4–2.7 and 2.4–2.6 for CMM3A and CMM3B, respectively, indicating optically thick dust emission and/or grain growth. A velocity gradient in the disk/envelope direction is detected for CMM3A in the CH3CN, CH3OH, and 13CH3OH lines detected in the 1.3 mm band, which can be interpreted as the rotation of the disk/envelope system. From this result, the protostellar mass of CMM3A is roughly evaluated to be 0.1–0.5 M ⊙ by assuming Keplerian rotation. The mass accretion rate is thus estimated to be 5 × 10−5 − 4 × 10−3 M ⊙ yr−1, which is higher than the typical mass accretion rate of low-mass protostars. The OCS emission line shows a velocity gradient in both outflow direction and disk/envelope direction. A hint of outflow rotation is found, and the specific angular momentum of the outflow is estimated to be comparable to that of the disk. These results provide us with novel information on the initial stage of a binary/multiple system.
Highlights
It is well known that a significant fraction of stars are born in binary or multiple systems (e.g., Duchene & Kraus 2013): the fraction is about a half for the solartype stars (Raghavan et al 2010)
A velocity gradient in the disk/envelope direction is detected for CMM3A in the CH3CN, CH3OH, and 13CH3OH lines detected in the 1.3 mm band, which can be interpreted as the rotation of the disk/envelope system
Since NGC2264 CMM3 is relatively close to the Sun and its structure can readily be investigated in detail, it may provide us with important information on the early stage of intermediate-mass protobinary systems
Summary
It is well known that a significant fraction of stars are born in binary or multiple systems (e.g., Duchene & Kraus 2013): the fraction is about a half for the solartype stars (Raghavan et al 2010). We here report the case of the very young protostellar source in the high mass star forming region NGC 2264. A similar case showing the different spectral appearance between the binary components were reported for NGC 1333 IRAS4A (Lopez-Sepulcre et al 2017) For this source, it has been reported that the dust opacity causes the difference (Sahu et al 2019; De Simone et al 2020). For evaluation of the protostellar mass and characterization of the disk/envelope structure for each component, we have observed the CMM3 region with ALMA at an angular resolution of about 0. We have investigated the kinematics of CMM3A by using molecular lines to evaluate its protostellar mass This observation will provide us with a clue to discriminating the above possibilities for the different spectral appearance between the two components raised by Watanabe et al (2017)
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