Astron. Astrophys. 343, L83-L86 (1999)

Letter to the Editor

The H₂O abundance and star formation history in Oph ^*

René Liseau and Göran Olofsson

Stockholm Observatory, S-133 36, Saltsjöbaden, Sweden (rene; olofsson@astro.su.se)

Received 15 December 1998 / Accepted 14 February 1999

Abstract

ISO -LWS observations towards a large number of different positions in the core of the are used to place a limit to the abundance of wide spread H₂O. From NLTE excitation and radiative transfer modelling the average line spectrum of the , we find X(H₂O) 10 to 10. We interprete these results within the framework of the dynamical chemistry models by Bergin, Melnick & Neufeld (1998), which describe the time evolution of molecular clouds being shocked by outflowing gas from young stellar objects, and conclude that the has been forming stars for less than one million years (2 - 5 yr). Finally, we show that this limiting result can be put to conclusive observational test by the ODIN satellite mission in the near future.

Key words: ISM: individual objects: ae Oph cloud (L 1688) ISM: clouds ISM: abundances ISM: molecules ISM: jets and outflows stars: formation

* 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) and with the participation of Isas and Nasa.

Send offprint requests to: R. Liseau

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Contents

• 1. Introduction
• 2. Observations and results
• 3. The H₂O abundance in the Oph cloud
• 4. The star formation history of the Oph cloud
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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