Broad-band optical polarimetric studies towards the Galactic young star cluster Berkeley 59

Abstract

We present multiwavelength optical linear polarimetric observations of 69 stars towards the young open cluster Berkeley 59. The observations reveal the presence of three dust layers located at distances of ∼300, ∼500 and ∼700 pc. The dust layers produce a total polarization P_V∼ 5.5 per cent. The mean values of polarization and polarization angles due to the dust layers are found to increase systematically with distance. We show that polarimetry in combination with the (U−B)–(B−V) colour–colour diagram yields a better identification of cluster members. The polarization measurements suggest that the polarization due the intracluster medium is ∼2.2 per cent. An anomalous reddening law exists for the cluster region, indicating a relatively larger grain size than that in the diffuse interstellar medium. The spatial variation of polarization and colour excess E(B−V) are found to increase with radial distance from the cluster centre, whereas θV and λmax are found to decrease with increasing radial distance from the cluster centre. About 40 per cent of cluster members show the signatures of either intrinsic polarization or rotation in their polarization angles. There is an indication that the starlight of the cluster members might have been depolarized because of non-uniform alignment of dust grains in the foreground dust layers and in the intracluster medium.