AAS 197, January 2001
Session 10. Low Mass Star Formation
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

## [10.06] Large Scale Variability Survey of Orion II: mapping the young, low-mass stellar populations

C. Briceño (CIDA), N. Calvet, L.W. Hartmann (CfA), A.K. Vivas (Yale University)

We present further results of our ongoing large scale variability survey of the Orion OB1 Association, carried out with the 8k \times 8k CCD Mosaic Camera on the 1m Schmidt telescope at the Venezuela National Observatory.

In an area of over 60 square degrees we have unveiled new populations of low-mass young stars over a range of environments, from the dense molecular clouds of the Orion belt region, Ori OB 1b, to areas devoid of gas in Orion OB 1a. These new young stars span ages from 1-2 Myr in Ori OB 1b to roughly 10 Myr in Ori OB 1a, a likely scenario of sequential star formation triggered by the first generation of massive stars. \\ Proxy indicators like H\alpha emission and near-IR excesses show that accretion from circumstellar disks in the 10 Myr stars of Ori OB 1a has mostly stopped. This population is a numerous analog of groups like TW Hya, making it an excellent laboratory to look for debris disks and study the epoch of planet formation in sparse, non-clustered environments.

Research reported herein funded by NSF grant No. 9987367, and by CONICIT and Ministerio de Ciencia y Tecnolog{\'i}a, Venezuela.