Accretion Disks in Cep OB2

I will present the identifications of young stars and disks in two
clusters in the Cep OB2 Association, Tr 37 (3-5 Myr) and NGC 7160 (10
Myr). Using a multi-wavelength approach, we have been able to identify the
low and high mass cluster members, as well as to study their disks and the
presence of accretion. In Tr 37, we have identified 135 low mass members
and 58 high and intermediate mass stars. In NGC 7160, we identified 45 low
mass members, and 68 high and intermediate mass members.

We use optical photometry (4Shooter/1.2m FLWO) and spectroscopy
(Hectospec/MMT) in order to identify and classify the low-mass members of
the clusters, to prove their youth (via Lithium absorption) and accretion
(via Halpha emission), and to determine their spectral types, extinctions,
and ages. We used the extinction to determine the membership of early G to
B stars. We study the presence and characteristics of their disks using
JHK photometry (2MASS), and Spitzer IRAC and MIPS data.

We obtain significant differences between these two clusters, indicative
of disk evolution in the age range from 3 to 10 Myr. Taking into account
the low mass stars (G-M2), ~40% of the Tr 37 members have disks, of which
all but 2 are accreting, whereas only one disk (accreting) has been
identified in NGC 7160. For the high and intermediate mass stars, we find
9 debris disks in Tr 37, plus 2 optically thick disks, whereas only 4
debris disks have been found in the  NGC 7160 sample. Comparison of disks
in Tr 37 with those of younger clusters (i.e., Taurus) seem to indicate
that disk emission is reduced at the age of 3-5 Myr, suggesting disk
evolution. Moreover, we find 2 "transition objects" in
Tr 37 which show disks at 5.8,8.0 and 24 microns, but no signs of
accretion. These results point out the importance of the study of these
clusters to understand disk evolution and dissipation at the epoch of planet
formation.