Photometric and polarimetric studies towards NGC 1931

Abstract

We investigated the dust properties and magnetic feld orientation towards the star cluster NGC 1931. Cluster members have been identified using both optical color-color as well as QV −UV stokes plane diagrams. Thus identified probable cluster members have been used to estimate the distance to the cluster NGC 1931 which is found to be 2.3±0.3 kpc. Few young stellar objects with possible intrinsic polarization have been identified. One-dimensional surface stellar density contours suggest two clustering in the NGC 1931 region. The reddening E(B − V ) is found to be variable between 0.50 to 0.90 mag. Polarimetric and photometric results indicate for the presence of slightly bigger dust grains within the intra-cluster medium. Although our previous work (Eswaraiah et al. 2011) reveals uniform dust grain alignment in the foreground medium towards the direction of NGC 1931, the polarization eficiency is found to be less than that of the general diffuse interstellar medium. This could be due to the normal extinction law in the foreground medium and anomalous reddening law in the intra-cluster medium.