Large HCO(+) and HCN abundances in the translucent cloud toward PKS 0528+134

Details Large HCO(+) and HCN abundances in the translucent cloud toward PKS 0528+134 Large HCO(+) and HCN abundances in the translucent cloud toward PKS 0528+134

Mar 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...441l..93h&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 441, no. 2, p. L93-L96

Astronomy and Astrophysics

Astronomy

37

Absorption Spectra, Abundance, Carbon Monoxide, Emission Spectra, Formyl Ions, Molecular Clouds, Radio Astronomy, Translucence, Astronomical Models, Carbon, Data Reduction, Quasars, Radio Observation, Spectrum Analysis, Sulfides

Scientific paper

Observations of (12)CO J = 1-0 (13)CO 1-0, HCO(+) 1-0, HCN 1-0, and CS 2-1 absorption against the quasar PKS 0528+134 obtained with the Owens Valley Millimeter Array (OVMA) are presented. The line of sight to this standard phase calibrator crosses the diffuse outer edge of the dark cloud B30, located in the lambda Ori ring of clouds. An excitation analysis of the absorption lines and (12)CO 1-0 emission yields an estimated H2 number density of nH2 = 100-500/cu cm, which is much lower than found for lines of sight studied previously by millimeter absorption lines. Surprisingly, HCO(+) and HCN are found to have abundances relative to (12)CO in this diffuse cloud which are comparable to or larger than those found in dark clouds. Significant differences in line width are found between (12)CO, HCN, and HCO(+) which cannot be attributed to line saturation. A possible explanation for the observed abundances and line widths involving cloud turbulence and the chemistry of CH(+) is proposed. It is concluded that HCO(+) absorption lines sample low-density regions which cannot be observed in molecular emission nor in CO millimeter absorption.

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