The H₂O abundance and star formation history in rho OPH

Abstract

Iso-Lws observations towards a large number of different positions in the core of the rho Ophc 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 rho Ophc, we find X(H₂O) < 10^{-6} to 10^{-5}. 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 rho Ophc has been forming stars for less than one million years (2 - 5x10⁵ yr). Finally, we show that this limiting result can be put to conclusive observational test by the Odin satellite mission in the near future. 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.