title: Hydrogen Emission Line n110 rarr n109: Detection at 5009 Megahertz in Galactic H II Regions.
abstract: The hydrogen emission line n(1l0) --> n(109) at the frequency 5009 megahertz which was predicted by Kardashev has been detected in M 17, Orion, and nine other galactic H II regions with the 42.7-m (140-foot) telescope and a 20-channel receiver at the National Radio Astronomy Observatory. The measured product of the half-power width of the line times the ratio of line-to-continuum brightness temperature is larger than that predicted by Kardashev's theory. The radial velocity obtained for M 17 and Orion agrees well with optical measurements. The search for a similar line of excited helium was without success.
authors.forename: B
authors.initials: B
authors.lastname: Höglund
authors.forename: P G
authors.initials: PG
authors.lastname: Mezger