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D. S. Balser (NRAO-GB), R. T. Rood (UVa), T. M. Bania (BU-IAR)
Helium is the most abundant element in the cosmos after hydrogen. It is thought to be produced in significant amounts during the era of primordial nucleosynthesis. Helium abundances in the interstellar medium are modified by processed material expelled by many generations of stars over the lifetime of the Galaxy. Therefore, present-day helium abundance measurements provide a net record of helium production and destruction.
Observations of 3He+ and 4He+ towards Galactic HII regions are discussed. The 3He+ emission is observed using the 8.7 GHz hyperfine transition. Radio recombination line emission of H and 4He have been made at X-band (8.5 GHz) and K-band (18 GHz) to provide information on y+ (4He+/H+) at different spatial resolutions. The 4He+ data are primarily used to understand the ionization properties of these HII regions. This is a crucial step in calculating the total 3He/H abundance ratio.
The research was supported by the National Science Foundation (AST 97-31484)