A multiwavelength polarimetric study towards the open cluster NGC 1893

Abstract

We present multiwavelength linear polarimetric observations for 44 stars of the NGC 1893 young open cluster region along with V-band polarimetric observations of stars of four other open clusters located between l∼ 160° and 175°. We found evidence for the presence of two dust layers located at a distance of ∼170 and ∼360 pc. The dust layers produce a polarization PV∼ 2.2 per cent. It is evident from the clusters studied in this work that, in the Galactic longitude range from l∼ 160° to 175° and within the Galactic plane (|b| < 2°), the polarization angles remain almost constant, with a mean of ∼163° and a dispersion of 6°. The small dispersion in polarization angle could be due to the presence of a uniform dust layer beyond 1 kpc. Present observations reveal that in the case of NGC 1893, the foreground two dust layers, in addition to the intracluster medium, seem to be responsible for the polarization effects. It is also found that towards the direction of NGC 1893, the dust layer that exists between 2 and 3 kpc has a negligible contribution towards the total observed polarization. The weighted mean for percentage of polarization (P_max) and the wavelength at maximum polarization (λ_max) are found to be 2.59 ± 0.02 per cent and 0.55 ± 0.01 μm, respectively. The estimated mean value of λ_max indicates that the average size of the dust grains within the cluster is similar to that in the general interstellar medium. The spatial variation of the polarization is found to decrease towards the outer region of the cluster. In this work, we support the notion, as has already been shown in previous studies, that polarimetry, in combination with the (U−B)–(B−V) colour–colour diagram, is a useful tool for identifying non-members in a cluster.