Wednesday, 3rd May at 2.00pm @ the JAC

ABSTRACT: I will discuss new deep high angular resolution observations of the high-mass protostar NGC 7538 S obtained with BIMA and VLA and supplemented with single dish data from JCMT and FCRAO. I also present deep IRAC imaging with Spitzer, which were released in the archive last fall.

DETAILS: The star is detected by IRAC at 4.5, 5.8 and 8 micron, but not at 3.6 micron. The BIMA observations confirm that NGC 7538 S is surrounded by a rotating accretion disk, which drives a collimated free-free jet and a very young, hot molecular outflow approximately perpendicular to the rotating accretion disk. All optically thick molecules show strong red-shifted self-absorption due to infall of gas from the surrounding dense molecular cloud core. Infall is even seen towards IRS1 (a serendipitous result), which show a clear inverse P Cygni profile in HCO+ against the strong continuum emission at 89 GHz. The free-free emission associated with NGC 7538 S is faint, ~ 6 mJy, highly collimated, and has a flat spectral index (alpha ~ 0) from 6 cm to 1.3 cm. The continuum emission observed with BIMA is dominated by dust emission at all observed frequencies (72 GHz - 220 GHz) and seen not only from the disk, but also from the dense cold cloud core surrounding the disk. At 1.4 mm the emission from the accretion disk dominates and is resolved into an elliptical source with a size of ~ 8" x 3" centered on the IRAC 4.5 - 8 micron source, which coincides with OH/H2O maser position and the base of the VLA free-free emission. Evidence for rotation is seen in all optically thin molecular tracers, H13CN J = 1-0, HN13C J = 1-0, H13CO+ J = 1-0, and DCN J = 3-2, although several molecules, particularly DCN and H13CO+ are affected by the hot molecular outflow. CH3CN J = 11-10 shows the disk very clearly, but is severely affected by the outflow, especially at higher K-levels. The mass of the continuum 'disk' is ~ 85 Msun and the luminosity is ~10^4 Lsun at an assumed distance of 2.8 kpc. The enclosed mass estimated from H13CN in the inner, rotationally supported part of the disk, D = 5" (14,000 AU) is 14 - 24 Msun/sini^2.