Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985natur.315..647a&link_type=abstract
Nature (ISSN 0028-0836), vol. 315, June 20, 1985, p. 647-649.
Astronomy and Astrophysics
Astronomy
12
Absorption Spectra, Astronomical Spectroscopy, Cassiopeia A, Radio Sources (Astronomy), Line Spectra, Recombination Reactions, Spectral Line Width
Scientific paper
The absorption line at 26 MHz observed by Konovalenko and Sodin (1980) towards Cas A was interpreted by Blake et al. (1980) as the 631-alpha recombination line due to carbon or heavier elements. This was confirmed subsequently by Konovalenko and Sodin (1981), who detected the 640-alpha line at the same optical depth as the 631-alpha line, within error limits. These lines represent the highest excited states yet detected in interstellar gas and could provide a unique diagnostic of conditions in diffuse clouds if observed over a range of frequencies. New observations of these lines carried out near 26, 38, 52 and 68 MHz using the National Radio Astronomy Observatory (NRAO) 91-m telescope at Green Bank are reported. Absorption lines at all these frequencies were detected, with a striking fourfold increase in width towards low frequencies due to collisional or radiation broadening. Assuming that these are recombination lines of carbon, the observed radial velocity corresponds well with that of the H I, OH, NH3 and H2CO absorption features that originate in the Perseus arm in the same direction.
Anantharamaiah K. R.
Erickson William C.
Radhakrishnan Venkatesh
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