Hydrogen Emission Line n ₁₁₀ → n ₁₀₉ : 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.

The Excited Atomic Hydrogen Lines 126a and 127a in HII Regions

“…The approximate range of the optical velocities is also marked in Figure 3. Weedman (1966) has shown that if these optical data are considered as distributed over the area of the aerial beam (6'·4 arc) of Hoglund and Mezger (1965) and are subject only to optical instrumental broadening effects a Gaussian profile similar to the radio case will result. The width measured by Hoglund and Mezger was 29 km/sec, but other observers report widths near 38 km/sec for the Orion Nebula (Table 2).…”

“…Several authors (Hoglund and Mezger 1965;Lilley et ai. 1966;Palmer and Zuckerman 1966;Penfield, Palmer, and Zuckerman 1967) have used the product of these two quantities to compute the electron temperature of HII nebulae.…”

The Green Bank Telescope Galactic H Ii Region Discovery Survey

“…Modern Galactic H II region surveys began with studies of the Palomar optical survey plates (Sharpless 1953(Sharpless , 1959. Radio recombination lines (RRLs) from Galactic H II regions were discovered in 1965 during the commissioning of the NRAO 140 Foot telescope; Höglund & Mezger (1965) detected H 109 α emission at 6 cm wavelength from M 17 and Ori A. Because the Galactic ISM is optically thin at centimeter wavelengths, RRL surveys were able to discover large numbers of H II regions distributed throughout the entire Galactic disk.…”

Interstellar Molecules and Dense Clouds

“…1, a-h, do not coincide exe represents radial actly in velocity. This effect probably ome from the fol-reflects the tendency of differences in ), b (108), c (89), the formation and excitation conditions 19), g (109). The s a line resulting to favor emission or absorption from r an electron with different molecules in slightly different positions within the cloud.…”