AAS 198th Meeting, June 2001
Session 41. The Milky Way Galaxy
Display, Tuesday, June 5, 2001, 10:00am-6:30pm, Exhibit Hall

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[41.08] An Old Dog's Last Hunt

R. T. Rood (UVa), T. M. Bania (BU-IAR), D. S. Balser (NRAO-GB)

At 08:12:20 EDT, 19 July, 1999 the Green Bank 140 Foot Telescope of the National Radio Astronomy Observatory made its last scientific observation, having been given a 12 minute reprieve. That last 12 minute Total Power pair taken toward the H II region S159 to the untrained eye looks like a noise spectrum, like most of the other roughly 25,000 pairs we have obtained since 1982. However, careful examination revealed a hint of of a feature at the frequency of the H130\gamma recombination line. Our ``target,'' the much weaker hyperfine line of {}3{\rm He}+, is readily visible in the 11.8 hours of integration acquired toward S159 over the previous three nights. The fact that we could detect {}3{\rm He}+ in a mere 11.8 hour integration, or indeed that we would be observing an obscure H II region like S159 reflects both the dramatic improvement in receivers and our change in thinking since 1982. We take this time to reflect on the last days of a noble instrument and its contributions toward our knowledge of an isotope whose cosmic abundance can set important astrophysical constraints for theories of primordial nucleosynthesis and the chemical evolution of the Galaxy. The research was supported by the National Science Foundation (AST 97-31484).

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