Abstract
Abstract We report molecular line observations of the massive protostellar source G339.88-1.26 with the Atacama Large Millimeter/Submillimeter Array. The observations reveal a highly collimated SiO jet extending from the 1.3 mm continuum source, which connects to a slightly wider but still highly collimated CO outflow. Rotational features perpendicular to the outflow axis are detected in various molecular emissions, including SiO, SO2, H2S, CH3OH, and H2CO emissions. Based on their spatial distributions and kinematics, we find that they trace different parts of the envelope–disk system. The SiO emission traces the disk and inner envelope in addition to the jet. The CH3OH and H2CO emissions mostly trace the infalling-rotating envelope and are enhanced around the transition region between envelope and disk, i.e., the centrifugal barrier. The SO2 and H2S emissions are enhanced around the centrifugal barrier and also trace the outer part of the disk. Envelope kinematics are consistent with rotating-infalling motion, while those of the disk are consistent with Keplerian rotation. The radius and velocity of the centrifugal barrier are estimated to be about 530 au and 6 , respectively, leading to a central mass of about 11 M ⊙, consistent with estimates based on spectral energy distribution fitting. These results indicate that an ordered transition from an infalling-rotating envelope to a Keplerian disk through a centrifugal barrier, accompanied by changes of types of molecular line emissions, is a valid description of this massive protostellar source. This implies that at least some massive stars form in a similar way to low-mass stars via core accretion.
Highlights
Massive stars impact many areas of astrophysics, yet there is little consensus on how they form
We report observations by the Atacama Large Millimeter/Submillimeter Array (ALMA) of the massive protostellar source G339.88-1.26, revealing the transition from an infalling-rotating envelope to a Keplerian disk, identified by both kinematic and chemical patterns
The enhancement around the centrifugal barrier may be due to the accretion shock, but more importantly, it may be due to the broadened inner edge of the infalling-rotating envelope, which can be directly irradiated by the central source (e.g., Sakai et al 2017)
Summary
Massive stars impact many areas of astrophysics, yet there is little consensus on how they form. In the core accretion scenario, a transition from relatively ordered rotating infall of a massive core at scales of ∼103 au to a rotationally supported disk on scales of several × 102 au or even smaller is expected, and these different components may be highlighted by emissions of different molecules, similar to the case of lowmass star formation, though the particular molecules tracing the various components may be different from the case of lowmass star formation, due to different temperature, density, and shock conditions. We report observations by the Atacama Large Millimeter/Submillimeter Array (ALMA) of the massive protostellar source G339.88-1.26, revealing the transition from an infalling-rotating envelope to a Keplerian disk, identified by both kinematic and chemical patterns
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