Kaas, A. A. and Bontemps, S.
From Darkness to Light: Origin and Evolution of Young Stellar Clusters, ASP Conference Proceedings, Vol. 243. Edited by Thierry Montmerle and Philippe André. San Francisco: Astronomical Society of the Pacific, ISBN: 1-58381-081-1, 2001, p.367
We summarize the main results of a mid-IR photometric survey with ISO for a few nearby embedded clusters. The sensitivity and spatial resolution of ISOCAM provided a wonderful tool for studies of the youngest stellar clusters, which are still deeply embedded in their parent molecular clouds. Mid-IR photometry is found to be extremely efficient in finding all the young stellar objects (YSOs) with IR excesses, i.e. mainly T Tauri stars surrounded by circumstellar disks and also some Class I sources. The spatial distribution of these sources is highly clustered and even sub-clustered, with a tendency of stronger concentration for the younger regions. The improved samples of IR-excess YSOs appear complete down to 0.03 L_sun for the most nearby clusters. This gives constraints on the mass functions well into the brown dwarf domain. The first results show that the mass functions of these clusters are identical to the field star IMF derived by Kroupa et al. (1993) with a flattening of the mass function at M_star ~ 0.5 M_sun.