An Anomalous Extinction Law in the Cep OB3b Young Cluster: Evidence for
  dust processing during gas dispersal
  We determine the extinction law through Cep OB3b, a young cluster of 3000
stars undergoing gas dispersal. The extinction is measured toward 76 background
K giants identified with MMT/Hectospec spectra. Color excess ratios were
determined toward each of the giants using $V$ and $R$ photometry from the
literature, $g$,$r$,$i$ and $z$ photometry from SDSS and $J$, $H$, and $K_{s}$
photometry from 2MASS. These color excess ratios were the used to construct the
extinction law through the dusty material associated with Cep OB3b. The
extinction law through Cep OB3b is intermediate between the $R_{V} = 3.1$ and
$R_{V} = 5$ laws commonly used for the diffuse atomic ISM and dense molecular
clouds, respectively. The dependence of the extinction law on line-of-sight
$A_{V}$ is investigated and we find the extinction law becomes shallower for
regions with $A_{V} > 2.5$ magnitudes. We speculate that the intermediate dust
law results from dust processing during the dispersal of the molecular cloud by
the cluster.
