Detection and analysis of recombination line emissions from galactic HII regions

A survey of ten galactic HII regions provided the most extensive high frequency (near 8.6 GHz) recombination line data to date, with several of the sources being observed for these lines for the first time at such a short wavelength. Transitions detected were H91a, H114.S , H130Y, He9ia , and Hell43. Observations were conducted on the National Radio Astronomy Observatory’s 140* telescope at Green Bank, West Virginia employing a specially designed parametric amplifier system constructed in the Space Science Department at Rice University. Computers were programmed to determine the line parameters after manipulating the data taken over several days and during various observing runs to give the best signal to noise ratio. Both the detection system, and the computer analysis is discussed. The hydrogen line emissions were analyzed to determine the electron temperatures of the regions assuming conditions of local thermodynamic equilibrium (LTE). These temperatures were found to be lower than corresponding optically determined temperatures. An analysis was therefore performed based on non-LTE assumptions and the temperatures so derived were found to be within reasonable agreement with optical results. The implications of the assumptions involved are discussed