An Extinction Study of the Taurus Dark Cloud Complex

Abstract

We present a study of the detailed distribution of extinction in a region of the Taurus dark cloud complex. Our study uses new BVR images of the region, spectral classification data for 95 stars, and IRAS Sky Survey Atlas (ISSA) 60 and 100 μm images. We study the extinction of the region in four different ways, and we present the first intercomparison of all these methods, which are as follows: (1) using the color excess of background stars for which spectral types are known, (2) using the ISSA 60 and 100 μm images, (3) using star counts, and (4) using an optical (V and R) version of the average color excess method used by Lada et al. We find that all four methods give generally similar results—with important exceptions. As expected, all the methods show an increase in extinction due to dense dusty regions (i.e., dark clouds and IRAS cores) and a general increase in extinction with increasing declination, due to a larger content of dust in the northern regions of the Taurus dark cloud complex. Some of the discrepancies between the methods are caused by assuming a constant dust temperature for each line of sight in the ISSA extinction maps and not correcting for unexpected changes in the background stellar population (i.e., the presence of a cluster or Galactic gradients in the stellar density and average V-R color). To study the structure in the dust distribution, we compare the ISSA extinction and the extinction measured for individual stars. From the comparison, we conclude that in the relatively low-extinction regions studied, with 0.9<AV<3.0 mag (away from filamentary dark clouds and IRAS cores), there are no fluctuations in the dust column density greater than 45% (at the 99.7% confidence level), on scales smaller than 0.2 pc. We also report the discovery of a previously unknown open cluster of stars behind the Taurus dark cloud near R.A. 4h19m, decl. 27°30' (B1950).