Three-Colour Photometry in the Southern Coalsack

Abstract

Photometric data in the UBV system of 1060 stars in seven uniformly obscured regions of the Southern Coalsack have been obtained. These data are analysed by the method proposed by Becker. The photographic measures are based on a UBV photoelectric sequence extending to V = 14.4. Absorption is determined as a function of distance in each of the regions. The distance of the Coalsack is found to be 174±18 parsecs, its photographic absorption ranging from 0.7 to 2.4 magnitudes, and the minimum mass of the absorbing material is estimated to be 14 solar masses. Behind the nebula lies a clear region which extends to 800 parsecs. At greater distances obscuration again sets in, averaging 0.85 mag./kpc in the region 1 kpc to 6 kpc from the Sun.