Abstract
A MEASUREMENT of the neutral hydrogen absorption spectrum of the Cassiopeia A radio source can in principle give information about the interarm regions of the Milky Way because this source lies in (and probably on the far side of) the Perseus arm. Neutral hydrogen lying in the region between the local arm and the Perseus arm may therefore be detectable in absorption as well as in emission. A combination of the emission and absorption data can give the spin temperature of the interarm gas (for example, see ref. 1). During the Conference of Young European Radio Astronomers at Jodrell Bank in June 1969, I was encouraged to make these measurements in discussions with Dr U. Mebold. This report describes measurements of the Cassiopeia A spectrum made with higher precision than those already published2–4.
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References
Mebold, U., Beiträge z. Radioastronomie, 1, 97 (1969).
Muller, C. A., Astrophys. J., 125, 830 (1957).
Shuter, W. L. H., and Verschuur, G. L., Mon. Not. Roy. Astron. Soc., 127, 387 (1964).
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Davies, R. D., Booth, R. S., and Wilson, A. J., Nature, 220, 1207 (1969).
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DE JAGER, G. Cassiopeia A Absorption Spectrum and the Interarm Medium. Nature 225, 622–623 (1970). https://doi.org/10.1038/225622a0
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DOI: https://doi.org/10.1038/225622a0
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