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Session 41 - T Tauri Stars & Protostellar Regions.
Display session, Wednesday, June 11
South Main Hall,

[41.07] Ionized Gas in Sagittarius B2 Main on \sim0.06\arcsec (500 AU) Scales

C. G. De Pree (Agnes Scott College), W. M. Goss (NRAO), R. A. Gaume (USNO)

We have observed ionized gas in the Sagittarius B2 Main (Sgr B2 M) star forming region with \sim60 mas (500 AU) resolution using the Very Large Array (VLA) in ``fast-switching'' mode at 7 mm. These images have 40 times the resolution of the best published images at this wavelength. These high resolution observations have revealed extremely high emission measures (EM\geq10^9 pc cm^-6) and rms electron densities (n_e\sim10^6 cm^-3) in the central four ultracompact HII (UCHII) regions (F1, F2, F3 and F4). Emission measures this high are expected if the long lifetime of UCHII regions is to be explained by pressure confinement by warm, dense molecular material. These observations also resolve complex, clumpy structures in the central four UCHII regions, and in one source (F3) a shell structure (d\sim0.01 pc). We have also imaged the same region in the H52\alpha radio recombination line at lower resolution (\sim0.5\arcsec), and source F3 is observed to have an extremely broad line width (\Delta V_FWHM\sim60 km s^-1). We propose a simple model for the F3 source, and examine the possibility that several of the other regions in Sgr B2 Main are pressure-confined UCHII regions.

Program listing for Wednesday