FORMING AN O STAR VIA DISK ACCRETION?

We present a study of outflow, infall, and rotation in a ~10 super(5) L sub([middot in circle]) star-forming region, IRAS 18360-0537, with Submillimeter Array and IRAM 30 m observations. The 1.3 mm continuum map shows a 0.5 pc dust ridge, of which the central compact part has a mass of ~80 M sub([middot in circle]) and harbors two condensations, MM1 and MM2. The CO (2-1) and SiO (5-4) maps reveal a biconical outflow centered at MM1, which is a hot molecular core (HMC) with a gas temperature of 320 + or - 50 K and a mass of ~13 M sub([middot in circle]). The outflow has a gas mass of 54 M sub([middot in circle]) and a dynamical timescale of 8 x 10 super(3) yr. The kinematics of the HMC are probed by high-excitation CH sub(3)OH and CH sub(3)CN lines, which are detected at subarcsecond resolution and unveil a velocity gradient perpendicular to the outflow axis, suggesting a disk-like rotation of the HMC. An infalling envelope around the HMC is evidenced by CN lines exhibiting a profound inverse P Cygni profile, and the estimated mass infall rate, 1.5 x 10 super(-3) M sub([middot in circle]) yr super(-1), is well comparable to that inferred from the mass outflow rate. A more detailed investigation of the kinematics of the dense gas around the HMC is obtained from the super(13)CO and C super(18)O (2-1) lines; the position-velocity diagrams of the two lines are consistent with the model of a free-falling and Keplerian-like rotating envelope. The observations suggest that the protostar of a current mass ~10 M sub([middot in circle]) embedded within MM1 will develop into an O star via disk accretion and envelope infall.