Abstract
WE have measured the 18-cm OH absorption spectrum of Sagittarius A over a range of 6.4 Mc/s using the 60-ft. radio telescope of Harvard College Observatory. This frequency range covers both the 1,667 Mc/s F(2→2) and the 1,665 Mc/s F (1→1) transitions. The spectrum is dominated by two features at +40 km/sec and −120 km/sec with respect to the local standard of rest. Parts of this spectrum have been previously reported1–3, notably the feature at +40 km/sec4. We have also obtained an absorption spectrum for 1II = 4°, bII = 0°. The characteristics of the background continuum radiation near 18 cm and this absorption spectrum allow us to establish an upper limit on the state temperature of interstellar OH.
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