  We present multi-wavelength optical and infrared photometry of 170 previously
known low mass stars and brown dwarfs of the 5 Myr Collinder 69 cluster (Lambda
Orionis). The new photometry supports cluster membership for most of them, with
less than 15% of the previous candidates identified as probable non-members.
The near infrared photometry allows us to identify stars with IR excesses, and
we find that the Class II population is very large, around 25% for stars (in
the spectral range M0 - M6.5) and 40% for brown dwarfs, down to 0.04 Msun,
despite the fact that the H(alpha) equivalent width is low for a significant
fraction of them. In addition, there are a number of substellar objects,
classified as Class III, that have optically thin disks. The Class II members
are distributed in an inhomogeneous way, lying preferentially in a filament
running toward the south-east. The IR excesses for the Collinder 69 members
range from pure Class II (flat or nearly flat spectra longward of 1 micron), to
transition disks with no near-IR excess but excesses beginning within the IRAC
wavelength range, to two stars with excess only detected at 24 micron.
Collinder 69 thus appears to be at an age where it provides a natural
laboratory for the study of primordial disks and their dissipation.
