Radio observations of D I and fractionation

Details Radio observations of D I and fractionation Radio observations of D I and fractionation

Dec 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apjs...89..271h&link_type=abstract

Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 89, no. 2, p. 271-292

Astronomy and Astrophysics

Astronomy

21

Deuterium, Fractionation, Interstellar Matter, Molecular Clouds, Radio Astronomy, Abundance, Data Reduction, Density (Number/Volume), Doppler Effect, Formyl Ions, Radio Observation, Radio Spectra, Very Large Array (Vla)

Scientific paper

We report observations to detect the 327 MHz line of atomic deuterium in the primarily molecular clouds towards Cas A and Sgr A, making appropriate choices of spectral and spatial resolution. Our best results for Cas A, based on 1253 hr of observing with the 85 foot (26 m) Hat Creek telescope and 45 hr with the very large array (VLA), yield an upper limit for the fraction of deuterium in atomic form, D I, of 0.14. We present an approximate analytical analysis of deuterium fractionation in translucent clouds, which shows that gas-phase ion-molecule reactions, assisted by dust and HD line self-shielding, are efficient in converting deuterium to HD. We conclude that little atomic deuterium is present in the molecular clumps in the Cas A clouds and that much higher sensitivity observations would be required to detect 327 MHz line in molecular clouds. We have also attempted to detect the 72 GHz line of DCO(+) toward Cas A. The observed upper limit to the DCO(+)/HCO(+) ratio of approximately 0.03 is not much larger than our theoretical estimate, and the DCO(+) line should be detectable with existing instrumentation, unless the temperature of these clouds is much larger than usually assumed.

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