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Multi-wavelength polarimetric study towards the open cluster NGC 1893

We present multi-wavelength linear polarimetric observations for 44 stars of the NGC 1893 young open cluster region along with V-band polarimetric observations of stars of other four open clusters located between l ~160 to ~175 degree. We found evidence for the presence of two dust layers located at a distance of ~170 pc and ~360 pc. The dust layers produce a polarization Pv ~2.2%. It is evident from the clusters studied in the present work that, in the Galactic longitude range l ~160 to 175 degree and within the Galactic plane (|b| < 2 degree), the polarization angles remain almost constant, with a mean ~163 degree and a dispersion of 6 degree. The small dispersion in polarization angle could be due to the presence of uniform dust layer beyond 1 kpc. Present observations reveal that in case of NGC 1893, the foreground two dust layers, in addition to the intracluster medium, seems to be responsible for the polarization effects. It is also found that towards the direction of NGC 1893, the dust layer that exists between 2-3 kpc has a negligible contribution towards the total observed polarization. The weighted mean for percentage of polarization (Pmax) and the wavelength at maximum polarization (λmax) are found to be 2.59 \pm 0.02% and 0.55 \pm 0.01 \mum respectively. The estimated mean value of λmax 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 the present work, we support the notion, as already has been shown in previous studies, that polarimetry, in combination with (U-B)/(B-V) colour-colour diagram, is a useful tool for identifying non-members in a cluster.