Journal Article

Why <i>COBE</i> and CN spectroscopy cosmic background radiation temperature measurements differ, and a remedy

Sydney Leach

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 421, issue 2, pages 1325-1330
Published in print April 2012 | ISSN: 0035-8711
Published online March 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.20390.x
Why COBE and CN spectroscopy cosmic background radiation temperature measurements differ, and a remedy

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In 2004, the cosmic background radiation (CBR) temperature Tγ(CN) determined from interstellar CN absorption spectra was found to be 50 ± 20 mK higher than the COBE bolometer measured value. It was proposed that this was due, at least in part, to an error in the evaluation of the rotational components of the oscillator strengths of the rovibronic transitions corresponding to the CN B 2Σ+–X 2Σ+(0 − 0), R(0), R(1) and P(1) lines. Corrections to the standard Hönl–London (HL) rotational line intensity factors used were determined. New data on interstellar CN absorption show that Tγ(CN) is 29 ± 2 mK greater than the latest value of the cosmological CBR temperature, Tγ(COBE) = 2.72548 ± 0.00057 K. These new results and CN fluorescence lifetime data are shown to give similar derived values for improved HL corrections as well as providing further evidence for the intramolecular coupling between the relevant B 2Σ+ state rotational levels and close-lying levels of the A 2Π state which invalidates the standard HL factors. Revised HL factors may be required in future Tγ(CN) measurements, in particular in high-redshift sites, which cannot be studied by bolometric means.

Keywords: molecular processes; techniques: spectroscopic; ISM: molecules; cosmic background radiation

Journal Article.  4737 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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