The Radio-Frequency Line Spectrum of Atomic Hydrogen and its Applications in Astronomy.
Abstract
Formulae are obtained for the frequencies, transition probabilities, and natural widths of the discrete lines of atomic hydrogen that fall within the radio spectrum. Such lines are due to transitions within either the fine structure or the hyperfine structure of the energy levels. The conditions necessary for the formation of observable emission and absorption lines are examined. Thence an inquiry is made into which of the hydrogen lines are likely to be observable from astronomical systems. It is found that the sun may give a detectable absorption line at about tO,OO0 Mc/sec, corresponding to the 22S1/ /2 fine-structure transition, but that other solar lines are not likely to be observable. From the interstellar gas, the emission line already observed (i.e., the 1420 Mc/sec hyperfine-structure line) is probably the only detectable hydrogen line. The importance of this line in the study of the interstellar gas is discussed. Some general conclusions are drawn from the preliminary evidence regarding the motion and kinetic temperature of the regions of un-ionized hydrogen. The ratio data are used to obtain a measure of the product of "galactic thickness" and average hydrogen concentration.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 1952
- DOI:
- 10.1086/145533
- Bibcode:
- 1952ApJ...115..206W