| Issue |
A&A
Volume 430, Number 2, February I 2005
|
|
|---|---|---|
| Page(s) | 549 - 560 | |
| Section | Interstellar and circumstellar matter | |
| DOI | https://doi.org/10.1051/0004-6361:20040437 | |
| Published online | 20 January 2005 | |
The interstellar C
O/C
O ratio in the solar
neighbourhood:
The ρ Ophiuchus cloud
*
1
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
Observations of up to ten carbon monoxide (CO and isotopomers) transitions are
presented to study the interstellar C18O/C17O ratio towards 21 positions
in the nearby (
pc) low-mass star forming cloud ρ Oph.
A map of the C18O 
–0 distribution of parts of the cloud is also
shown.
An average 12C18O/12C17O 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 104 cm-3 to 
105 cm-3. Towards some lines of sight
C18O 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
Based on observations collected with the Swedish/ESO Submillimeter Telescope (SEST) at the European Southern Observatory, Chile (ESO 62.I-0752). All spectra (some of which are shown in Fig. [see full text]) are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/549
© ESO, 2005
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