A Detailed Study of the Accretion Disk Surrounding the High-mass Protostar NGC 7538 S

We present deep high-angular resolution observations of the high-mass protostar NGC 7538 S, which is in the center of a cold dense cloud core with a radius of 0.5 pc and a mass of ~2000 M _sun. These observations show that NGC 7538 S is embedded in a compact elliptical core with a mass of 85-115 M _sun. The star is surrounded by a rotating accretion disk, which powers a very young, hot molecular outflow approximately perpendicular to the rotating accretion disk. The accretion rate is very high, ~(1.4-2.8) × 10^-3 M _sun yr^-1. Evidence for rotation of the disk surrounding the star is seen in all largely optically thin molecular tracers, H¹³CN J = 1 → 0, HN¹³C J = 1 → 0, H¹³CO⁺ J = 1 → 0, and DCN J = 3 → 2. Many molecules appear to be affected by the hot molecular outflow, including DCN and H¹³CO⁺. The emission from CH₃CN, which has often been used to trace disk rotation in young high-mass stars, is dominated by the outflow, especially at higher K levels. Our new high angular resolution observations show that the rotationally supported part of the disk is smaller than we previously estimated. The enclosed mass of the inner, rotationally supported part of the disk (D ~ 5'', i.e., 14,000 AU) is ~14-24 M _sun.