Computer Science
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt.........4d&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL, 1996.Source: Dissertation Abstracts International, Volume: 57
Computer Science
Sagittarius B2
Scientific paper
In this thesis I present the results of an extensive multi-frequency, multiconfiguration observational program of four massive star-forming regions at different galactocentric radii using the Very Large Array (VLA). I have observed the luminous regions Sagittarius B2 (Sgr B2, near the Galactic center) and W49A (D = 11.4 kpc), and two smaller regions: K3-50 (D = 8.5 kpc) and NGC 6334 (D = 1.7 kpc). The VLA observations have spatial and spectral resolutions as high as 0.3^{''} and 3.5 km s^{-1}, respectively. These radio frequency continuum and recombination line observations have revealed important common characteristics between the regions, and have raised new questions about the earliest stages of massive star formation. Sensitive, multi-configuration radio images are required to properly classify source morphologies. Within each of the two largest regions (Sgr B2 and W49A), there is a striking variety of morphologies (spherical, bipolar, shell and "cometary") and a large number of resolved sources. In Sgr B2, 49 HII regions are detected within a ~ 2.5 pc radius, centered on the bright source F. The most compact HII regions in Sgr B2 (d ~ 0.01 pc) are spatially coincident with two known massive molecular outflows. In W49A, 45 regions are detected within a ~3.5 pc radius of the central source G. In each of the four studied regions I have also imaged the ionized gas kinematics, crucial to the interpretation of the morphologies observed. In K3-50A and NGC 6334A for example, continuum morphologies and velocity gradients consistent with bipolar ionized outflows have been detected. This study is the first in which both the line and continuum parameters for such a large number of sources have been examined. In a small number of sources I have detected very broad recombination lines (DeltaFWHM >= 60 km s^{-1}) and rising spectral indices (alpha ~ 1) at centimeter wavelengths. These sources are most likely very young, still coming into pressure equilibrium with their environments. I have used these VLA observations of the ionized and molecular gas along with existing molecular gas observations of these sources to address several issues, including: the lifetime paradox of ultracompact HII (UCHII) regions, Galactic helium abundances, ionized outflows from massive stars, and UCHII region evolution.
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