AAS 205th Meeting, 9-13 January 2005
Session 98 High Mass Star Formation and Deeply Embedded Star Formation
Poster, Wednesday, January 12, 2005, 9:20am-6:30pm, Exhibit Hall

## [98.02] High angular resolution observations of the high-mass protostar NGC 7538S

G. Sandell (SOFIA-USRA), M. Wright (UC Berkeley), W. M. Goss (NRAO)

We present deep high angular resolution images of the high-mass protostar NGC 7538S in CH3CN J=12-11, DCN J=3-2 and in 3 mm and 1.4 mm continuum obtained with BIMA at a resolution of 3.2''. We also present deep VLA images at angular resolutions of \leq 1'' at 6 cm, 3.6 cm, 2 cm and 1.3 cm, which show that the protostar drives a highly collimated ionized jet emerging from the center of the accretion disk. The CH3CN emission is hot; we detect lines up to K=6, but the emission at higher K-levels is dominated by the outflow. The size of the disk becomes smaller for each step up the K-ladder, i.e. we cannot assume that the transitions originate in the same volume of gas. The lower K-transitions are optically thick and display narrow self-absorption at slightly redshifted velocities up to K=3. The high optical depth is confirmed by detection of CH313CN K=2 and 3. Red-shifted self-absorption and high velocity emission is also seen in DCN, partly masking the underlying emission from the rotating accretion disk. These observations suggest a disk size of 5.5'' (15,000 A.U.). The rotation curve measured in DCN predicts an enclosed mass of 20 M\odot/sin2i.

This work was supported in part by NSF Grant AST 0228963 to the University of California.

Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.