Broadband Linear Polarization in the Region of the Open Star Cluster NGC 1817

TL;DR

This study presents multi-band polarimetric observations of stars in NGC 1817, revealing wavelength-dependent polarization mainly caused by interstellar dust, with insights into dust grain properties and spatial distribution in the cluster region.

Contribution

It provides the first detailed polarimetric analysis of NGC 1817, highlighting dust grain characteristics and spatial distribution differences between the core and corona regions.

Findings

Polarization peaks in V band with an average of 0.95%.

Dust grain size distribution similar to general interstellar medium.

Variable stars show slightly lower polarization than non-variable stars.

Abstract

Multi-band linear polarimetric observations of 125 stars in the region of the cluster NGC 1817 have been carried out intending to study properties of interstellar dust and grains in that direction. The polarization is found to be wavelength-dependent, being maximum in the V band with an average value of 0.95%. The foreground interstellar dust grains appear to be the main source of linear polarization of starlight toward the direction of NGC 1817. The average value of the position angle in the V band of 119.2 degree is found to be less than the direction of the Galactic parallel in the region, indicating that the dust grains in the direction are probably not yet relaxed. Spatial distribution of dust appears to be more diverse in the coronal region than the core region of the cluster. The maximum value of the degree of polarization is estimated to be 0.93% for members of the cluster using the Serkowski relation. The average value of wavelength corresponding to the maximum polarization of 0.54+/-0.02 micron indicates that the size distribution of dust grains in the line of sight is similar to that of the general interstellar medium. Several variable stars in the cluster were also observed for polarimetrically and pulsating variables appear to have a slightly lower value of polarization from other nonvariable member stars of the cluster. There are indications of the existence of dust layers existence in front of those clusters which are located close to galactic plane while for clusters located away from galactic plane no major dust layers are observed.