Gamma ray spectroscopy on long duration balloon flights in Antarctica

In the past twenty-five years a variety of gamma-ray lines have been detected from astrophysical sources. These include nuclear lines from nucleosynthesis in supernovae and from accelerated particles interactions at the Sun and in the Orion complex, the positron annihilation line and Compton-scattered features from transient black-hole candidate sources, and cyclotron lines from magnetized neutron star sources. High resolution gamma-ray spectroscopy can provide quantitative insight into the various physical processes occurring in these objects, but long observing times are required. Long duration balloon flights (LDBFs) in Antarctica presently provide the best platform for such measurements, outside of large, expensive spacecraft. Specific scientific objects that can be addressed by Antarctic LDBFs, and the capabilities and limitations of such flights are discussed. The HIgh REsolution Gamma-ray and hard X-ray Spectrometer (HIREGS), which has made three Antarctic LDBF's, is described and its results briefly discussed.