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

Abstract

SummaryForty radio sources have been observed for the presence of the hydrogen recombination lines 126", at 3248·708 MHz and 127", at 3172·864 MHz with a 6' arc aerial beam and a receiver with 48 channels of 37 kHz bandwidth each. Detections were made in 34 sources, all of which were either HI! regions or optically unidentified thermal sources.The mean ratio of line intensity to thermal continuum intensity was 3·4% (± 1· 3 % s.d.); the mean halfwidth of the lines was 340 kHz (± 50 kHz s.d.), which is equivalent to 31·5 km/sec in radial velocity.It is suggested that many of the profiles are complex and contain two or more major components that represent large·scale motions in the HI! regions. The Orion and Omega nebulae are shown to have this type of profile and are discussed in some detail.

Recombination Lines near 8·9 GHz of Strong Sources in the Southern Milky Way

“…Values of Te are derived from the expression (see e.g. McGee and Gardner 1968) TLAV_(41n2)t Table 4 are seen to fall between 6000 and 10000 K. They are similar to results obtained by Wilson et al (1970) from the H 109(;( lines: the average difference is 10 %.…”

“…The first survey of the radio recombination lines of southern HII regions was made by McGee and Gardner (1968), who investigated 40 sources and found lines in 34. Wilson et al (1970) made a comprehensive search and detected lines in 130 sources.…”

Recombination Lines 158a and 198ß in Nine Southern Nebulae

“…does not account for all the difference between the determinations from radio observations and the optically derived values of T e. This finding reinforces previous statements (McGee and Gardner 1968) that the observed profiles are quite often composites of two or more major sources of line radiation.…”

“…The results corroborate the measurements of radial velocity of the same objects made on the H 126a: line by McGee and Gardner (1968). Intensity ratios of the ,8 to a: lines are listed.…”

“…The H 158a line was also observed with 10 kHz bandwidth, and in both cases good agreement was obtained with the H 126a recombination line (McGee and Gardner 1968).…”