The CIDA-QUEST large-scale survey of Orion OB1:: Evidence for rapid disk dissipation in a dispersed stellar population

We are conducting a large-scale, multiepoch, optical photometric survey [Centro de Investigaciones de Astronomia-Quasar Equatorial Survey Team (CIDA-QUEST)] covering about 120 square degrees to identify the young low-mass stars in the Orion OB1 association. We present results for an area of 34 square degrees. Using photometric variability as our main selection criterion, as well as follow-up spectroscopy, we confirmed 168 previously unidentified pre-main sequence stars that are about 0.6 to 0.9 times the mass of the sun (M-.), with ages of about 1 million to 3 million years (Ori OB1b) and about 3 million to 10 million years (Ori OB1a). The Low-mass stars are spatially coincident with the high-mass (at Least 3 M-.) members of the associations. Indicators of disk accretion such as H alpha emission and near-infrared emission from dusty disks fall sharply from Ori OB1b to Ori OB1a, indicating that the time scale for disk dissipation and possibly the onset of planet formation is a few million years.