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Astron. Astrophys. 347, L1-L4 (1999)

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Letter to the Editor

Large atomic oxygen abundance towards the molecular cloud L1689N *

E. Caux 1, C. Ceccarelli 2, A. Castets 2, C. Vastel 1, R. Liseau 3, S. Molinari 4, B. Nisini 5, P. Saraceno 6 and G.J. White 7,3

1 CESR CNRS-UPS, B.P. 4346, F-31028 Toulouse Cedex 04, France
2 Laboratoire d'Astrophysique, Observatoire de Grenoble - B.P. 53, F-38041 Grenoble Cedex 09, France
3 Stockholm Observatory, S-133 36 Saltsjöbaden, Sweden
4 IPAC/Caltech, MS 100-22, Pasadena, CA, USA
5 Osservatorio Astronomico di Roma, via Frascati 33, I-00044 Monte Porzio, Italy
6 Instituto di Fisica dello Spazio Interplanetario - CNR, area di ricerca Tor Vergata, via Fosso del Cavaliere, I-00133 Roma, Italy
7 Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK

Received 7 May 1999 / Accepted 7 June 1999


We present spectroscopic ISO-LWS observations of the [OI] (63 µm and 145 µm), the [CII] (158 µm) and the H2O (179 µm) lines towards the molecular cloud L1689N. From the observed ratio of the two [OI] lines, we deduce a mean gas temperature of (26 [FORMULA]0.5) K, an H2 density [FORMULA] cm-3 and an [OI] column density [FORMULA] cm-2. Combining these observations with previous CO observations, we obtain [OI]/[CO] [FORMULA] 50. This ratio implies that up to 98% of oxygen abundance is in atomic form in the gas phase. Furthermore, assuming all the gaseous carbon is locked into the CO, carbon has to be depleted by more than a factor 24. Finally, the upper limit derived for the H2O (179 µm) line ([FORMULA] erg s-1 cm-2) implies that the water abundance in this region is less than [FORMULA] with respect to H nuclei.

Key words: stars: formation – ISM: jets and outflows – ISM: individual objects: L1689N – infrared: ISM: lines and bands

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA.

Send offprint requests to: Emmanuel.Caux@cesr.fr

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© European Southern Observatory (ESO) 1999

Online publication: June 18, 1999