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Issue A&A Volume 430, Number 2, February I 2005 Page(s) 549 - 560 Section Interstellar and circumstellar matter DOI 10.1051/0004-6361:20040437

A&A 430, 549-560 (2005)
DOI: 10.1051/0004-6361:20040437

The interstellar C O/C O ratio in the solar neighbourhood: The  Ophiuchus cloud

J. G. A. Wouterloot^{1, 2}, J. Brand³ and C. Henkel<sup>4

1</sup>  Joint Astronomy Centre, 660 N. A'ohoku Place, University Park, 96720 Hilo, Hawaii, USA
    e-mail: j.wouterloot@jach.hawaii.edu
²  Radioastronomisches Institut, Univ. Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
³  Istituto di Radioastronomia, CNR, via Gobetti 101, 40129 Bologna, Italy
⁴  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

(Received 13 March 2004 / Accepted 15 September 2004)

Abstract
Observations of up to ten carbon monoxide (CO and isotopomers) transitions are presented to study the interstellar C ¹⁸O/C ¹⁷O ratio towards 21 positions in the nearby ( pc) low-mass star forming cloud  Oph. A map of the C ¹⁸O J=1-0 distribution of parts of the cloud is also shown. An average ¹²C ¹⁸O/ ¹²C ¹⁷O isotopomeric ratio of , reflecting the ¹⁸O/ ¹⁷O isotope ratio, is derived from Large Velocity Gradient (LVG) calculations. From LTE column densities we derive a ratio of . These calculations also show that the kinetic temperature decreases from about 30 K in the cloud envelope to about 10 K in the cloud cores. This decrease is accompanied by an increase of the average molecular hydrogen density from 10 ⁴ cm ^-3 to 10 ⁵ cm ^-3. Towards some lines of sight C ¹⁸O optical depths reach values of order unity.

Key words: ISM: abundances -- ISM: clouds -- ISM: molecules -- Galaxy: abundances -- radio lines: ISM -- ISM: individual objects: rho Oph

SIMBAD Objects

© ESO 2005

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