Chi-Hung Yan, ASIAA, Taiwan. From Circumstellar to Protoplanetary Disk : WIRCam/Spitzer YSO Survey toward rph961; Ophiuchus Abstract: Studying the process of low-mass star formation is a key for understanding the formation and evolution of our solar system. The lifetime, evolution of circumstellar disks and the disk rate of cluster stars all play important roles during the formation of a planetary system. By collecting large amount of spectral energy distribution (SED) of young stellar objects (YSO), one is able to analyze YSO properties in a statistical manner. In this project, we aim to study YSO properties along with their evolution in molecular clouds, as well as the ambient environment by using a newly developed SED fitting tool. Together with Spitzer IRAC/MIPS catalog, we have carried out a wide field YSO survey toward the star forming region, rho961; Oph. It is one of the nearby star formation regions with age less than 1 Myr and distance 125 ~ 130 pc. Using our SED analysis technique, we detected more YSO candidates, and their population indicated that the lifetime should be longer than predicted. The population of different YSOs provide unique information on disk evolution. We plan to identify sources with signatures of planet-forming systems for follow-up observation in near future.