Dust Extinction and Molecular Cloud Structure: L977

We report results of a near--infrared imaging survey of L977, a dark cloud inCygnus seen in projection against the plane of the Milky Way. We usemeasurements of the near--infrared color excess and positions of the 1628brightest stars in our survey to measure directly dust extinction through thecloud following the method described by Lada et al. (1994). We spatiallyconvolve the individual extinction measurements with a square filter 90" insize to construct a large-scale map of extinction in the cloud. We derive atotal mass of M(L977)= (660 +/- 30)(D/500 pc)^2 Msun and, via a comparison ofsource counts with predictions of a galactic model, estimate a distance to L977of 500 +/- 100 pc. We find a correlation between the measured dispersion in ourextinction determinations and the extinction. We interpret this as evidence forthe presence of structure on scales smaller than the 90" resolution of ourextinction map. To further investigate the structure of the cloud we construct the frequencydistribution of the 1628 individual extinction measurements in the L977 cloud.The shape of the distribution is similar to that of the IC 5146 cloud. MonteCarlo modeling of this distribution suggests that between 2 < Av < 40 mag (orroughly 1 < r < 0.1 pc) the material inside L977 is characterized by a densityprofile n(r) \propto r^(-2). Direct measurement of the radial profile of aportion of the cloud confirms this result. (more...)Comment: 37 pages, 12 figures (10 embedded in text + 2 in jpeg format). Accepted by The Astrophysical Journa