From a study of the early-type stars in the region of the long-period cepheid RS Puppis, Westerlund (1963) suggested the existence of an OB association (Puppis OB III) in this direction (, ) at a distance of about 1700 pc. The age of the association was estimated to be yrs. It is situated in a volume of space that is rich in dust as well as gas. The association has an angular diameter of about 5 degrees and contains the emission nebulae Gum 10 = RCW 19 and Gum 11 = RCW 20 = NGC 2579 (Gum 1955; Rodgers, Campbell & Whiteoak 1960). In a wide latitude CO survey of the third galactic quadrant, May et.al. (1988) identified a molecular cloud feature at , v= 35 km s-1 to be associated with Puppis OB III and the HII region RCW 19. The kinematic distance of this molecular cloud is 3.3 kpc.
Westerlund (1963) gave a list of 31 OB type stars brighter than within about 3 degrees from RS Puppis. From the colour - magnitude diagram for these stars, it was suggested that 23 of them are members of an OB association and the rest were assumed to be field stars. In this paper we present the results of optical linear polarization measurements of all the 31 stars in the list of Westerlund (1963). The association members are found to have higher values of polarization when compared with the field stars. We produce a polarization map for this region and study the relationship between the degree of polarization and reddening for stars in the direction of the OB association.
© European Southern Observatory (ESO) 1998
Online publication: February 16, 1998