Optical polarimetric study of open clusters: distribution of interstellar matter towards NGC 654

ABSTRACT We present new B,V and R linear polarimetric observations for 61 starstowards the region of the young open cluster NGC 654. In this study we foundevidence for the presence of at least two layers of dust along the line of sight tothe cluster. The distances to the two dust layers are estimated to be ∼ 200 pcand ∼ 1 kpc which are located much closer to the Sun than the cluster (∼ 2.4kpc). Both the dust layers have their local magnetic field orientation nearlyparallel to the direction of the Galactic plane. The foreground dust layer isfound to have a ring morphology with the central hole coinciding with thecenter of the cluster. The foreground dust grains are suggested to be mainlyresponsible for both the observed differential reddening and the polarizationtowards the cluster.Keywords: polarization-dust, extinction-openclustersandassociations:individual:NGC 654 1 INTRODUCTIONThe wavelength dependence of interstellar extinction and polarization provides constraintson the characteristics of interstellar grains. Interstellar polarization strongly varies withwavelength (Serkowski, Mathewson & Ford 1975; Wilking et al. 1980). In particular, thewavelength of maximum interstellar polarization (λ