A Multi-wavelength survey of the Young Stellar Cluster Cep OB3b

We present results from an extensive multi-wavelength survey of Cep OB3b, one of the largest young clusters within 1 kpc of the Sun. We estimate that Cep OB3b has a membership of approximately 3000 young stars in a region of 10 x 7 pc (Allen et al. 2012). Similar in membership and overall size to the Orion Nebular Cluster, Cep OB3b is older and more evolved, with most of the young stars located in a cavity with a V-band extinction of less than 2.5 magnitudes. Star formation is still occurring in the molecular clouds that border the cavity. Literature age estimates for this region give a range between 3 Myr and 6 Myr (Mayne et al. 2007, Littlefair et al. 2010, Bell et al. 2013). We have compiled an extensive multi-wavelength database of candidate member young stars that are well characterized with spectral types, bolometric luminosities, masses, isochronal ages, X-ray properties and the presence (or lack) of a disk. To construct a precise HR diagram for ~700 cluster members, we derive an extinction law for this region between 500 nm and 2.2 micron and find it intermediate between that of dense clouds (Rv ~ 5) and that of the diffuse ISM (Rv ~ 3). Using the Siess (2000) models and assuming a distance of 700 pc give an isochronal age of 2 Myr. We find that certain cluster properties, such as the disk fraction and rotation period distribution, vary spatially across the cluster. We analyze whether these variations are due to environmental differences (such as nearby massive O stars) or a mixture of ages in the cluster. In the case of the disks, we conclude that the variations are due to a mixture of ages.