OH Absorption Spectra in Sagittarius

• DOI: 10.1038/203065a0
• Publication Date: 2006-07-05T17:50:36Z
• Authors: S. J. GOLDSTEIN; E. J. GUNDERMANN; A. A. PENZIAS; A. E. LILLEY

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.