LOW-MASS YOUNG STARS IN CEP OB2: AGES, DISTRIBUTION AND ACCRETION DISKS AURORA SICILIA-AGUILAR 1 , LEE HARTMANN 1 ,C ´ ESAR BRICE ˜ NO 2 , MAR ´ IA EUGENIA CONTRERAS 3 , JAMES MUZEROLLE 4 and NURIA CALVET 1 1 Smithsonian Astrophysical Observatory, Cambridge, MA, U.S.A.; E-mail: asicilia@cfa.harvard.edu 2 Centro de Investigaciones de Astronom´ ıa, Venezuela 3 Universidad Aut´ onoma de M´ exico, Mexico 4 University of Arizona, U.S.A. Abstract. We are studying the young clusters Tr37 and NGC7160 in the Cep OB2 region as part of a program to understand the evolution of accretion disks at the ages of disk dissipation and planet formation. Here, we present the first identifications of low mass (spectral types K-M) members of the clusters and study the presence and characteristics of their accretion disks, finding evidences of disk evolution. Using optical photometry and spectroscopy, we have identified ∼70 members in Tr37 and ∼20 in NGC7160, confirming age estimates of 3 and 10 Myr respectively. Accretion rates are ∼10 −8 M ⊙ yr −1 in Tr37. We have not found any accreting members in NGC7160, suggesting that disk accretion generally ends before the age of 10 Myr, which is consistent with the results from other populations. Keywords: T Tauri stars, accretion disks, disk evolution, protoplanetary disk, planet formation, star formation 1. The Cep OB2 Region The Cep OB2 region contains two of the most promising young clusters, (Tr37 and NGC7160) for finding young stars at the ages critical for disk dissipation and planet formation. It contains a ∼50pc radius bubble-shaped structure, which is seen in atomic and molecular gas, centered at the cluster NGC7160. The cluster Tr37 is located at the edge of the bubble and contains the O6 star HD206267. Cep OB2 shows many associated HII regions and gas structures(Garrison and Kormendy, 1976; Simonson and van Someren Greve, 1976; ´ Abrah´ am et al., 2000). The study of the dynamics of the gas (Patel et al., 1995, 1998) gives an age estimation of 3-5 Myr for Tr37, and the high mass members (Contreras et al., 2002) are consistent with this age and give an approximate distance of 900 pc. 2. Identifying Young Stars We took optical (VRI) and U band images of the clusters NGC7160 and Tr37 using 4Shooter camera at the 1.2 m telescope in Fred Lawrence Whipple Observatory Astrophysics and Space Science 292: 457–463, 2004. C  2004 Kluwer Academic Publishers. Printed in the Netherlands.