Star formation in the ρ Ophiuchi cloud

The recent star formation activity in the rho Ophiuchi region is almost limited to the two main clouds L1688 and L1689. Seen from a large scale perspective, the rho Ophiuchi cloud is associated with the Upper Sco OB association, suggesting that the presently observed star formation is either a triggered, secondary event or the end of a long term (similar to 5 Myr) activity which tias been also forming the OB land the accompanying low-mass) stars of the association. Using ISOCAM results I show that the recent star formation occurred essentially within the known dense cores of the rho Ophiuchi molecular cloud where the star formation efficiency might be as high as 30 %. This tight association explains the general behavior of young stars to form in clusters, and supports the relevance of the investigations for the initial conditions of star formation within the so-called dense cores. ISOCAM data are also used to derive a new mass function of the newly formed stars in rho Ophiuchi which demonstrates a clear flattening below M-* similar to 0.5 M.. The observed flattening is consistent with the results obtained for the field star initial mass function. This finding supports the concept of an unique IMF for the overall Galactic star formation.