  Using far-infrared emission maps taken by IRAS and Spitzer and a
near-infrared extinction map derived from 2MASS data, we have made dust
temperature and column density maps of the Perseus molecular cloud. We show
that the emission from transiently heated very small grains and the big grain
dust emissivity vary as a function of extinction and dust temperature, with
higher dust emissivities for colder grains. This variable emissivity can not be
explained by temperature gradients along the line of sight or by noise in the
emission maps, but is consistent with grain growth in the higher density and
lower temperature regions. By accounting for the variations in the dust
emissivity and VSG emission, we are able to map the temperature and column
density of a nearby molecular cloud with better accuracy than has previously
been possible.
