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Identification of the anomalous 26.131-MHz nitrogen line observed towards Cas A

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Abstract

Konovalenko and Sodin1 recently reported the detection of an absorption line at a frequency of 26.131 MHz towards Cassiopeia A and attributed the line to the 26.127 MHz F = 5/2 → 3/2 hyperfine transition of 14N. The difference in frequency corresponds to a radial velocity of –40 km s–1, which is compatible with the mean velocity of the Perseus arm H I absorption lines seen towards Cas A. However, to explain the strength of the line, Konovalenko and Sodin require (N/H) = 8 × 10–3 compared with the cosmic ratio of 1.2 × 10–4. An anomalous abundance of this magnitude would have substantial impact on ideas about galactic nucleosynthesis. We suggest here that the line is a 631α recombination line due to neutral atoms of heavy elements—either carbon atoms in the H I clouds or possibly heavier atoms (Mg, Ca, Fe) in hot (∼104 K) ionized gas along the line of sight to Cas A.

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Authors and Affiliations

  1. Electrical Engineering Department, University of Illinois,

    David H. Blake

  2. Astronomy Department, University of Illinois,

    Richard M. Crutcher

  3. Physics Department and Astronomy Department, University of Illinois, Urbana, Illinois, 61801

    William D. Watson

Authors
  1. David H. Blake
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  2. Richard M. Crutcher
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  3. William D. Watson
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Blake, D., Crutcher, R. & Watson, W. Identification of the anomalous 26.131-MHz nitrogen line observed towards Cas A. Nature 287, 707–708 (1980). https://doi.org/10.1038/287707a0

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  • DOI: https://doi.org/10.1038/287707a0

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