EDP Sciences
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Volume 367, Number 3, March I 2001
Page(s) 995 - 999
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20000499

A&A 367, 995-999 (2001)
DOI: 10.1051/0004-6361:20000499

Absorption against the cosmic 2.7 K background

S. Chandra1, 2 and W. H. Kegel2

1  School of Physical Sciences, S.R.T.M. University, Nanded 431 606, India
2  Institut für Theoretische Physik, J.W. Goethe-Universität, 60054 Frankfurt am Main, Germany

(Received 25 February 2000 / Accepted 12 December 2000 )

Two interstellar lines, 1 $_{10}\rightarrow$ 111 of formaldehyde at 4.831 GHz, and 2 $_{20}\rightarrow$ 211 of cyclopropenylidene at 21.590 GHz, have so far been observed in absorption against the cosmic 2.7 K background. Observation of an interstellar line in absorption against the cosmic 2.7 K background is an unusual phenomenon, and can only be possible under rather peculiar conditions developed in the molecule, generating the line. We predict that two more lines, 3 $_{30}\rightarrow$ 321 at 27.100 GHz, and 3 $_{31}\rightarrow$ 322 at 59.550 GHz of cyclopropenylidene, and three lines, 2 $_{20}\rightarrow$ 211 at 15.600 GHz, 3 $_{30}\rightarrow$ 321 at 23.100 GHz, and 3 $_{31}\rightarrow$ 322 at 39.700 GHz of ethylene oxide, may show absorption against the cosmic 2.7 K background. We speculate that such peculiar conditions are characteristic for b-type asymmetrical top molecules. -The observation of these lines may be used to place upper bounds to the density in the absorbing region.

Key words: molecular processes -- ISM: molecules -- Cosmology: cosmic microwave background -- radio lines: ISM

Offprint request: W. H. Kegel, kegel@astro.uni-frankfurt.de

SIMBAD Objects in preparation

© ESO 2001