Polarization, polarizing efficiency, and grain alignment towards the direction of the cluster NGC 2345

Abstract

We have investigated the grain alignment and dust properties towards the direction of the cluster NGC 2345 using the multi-band optical polarimetric observations. For the majority of the stars, the observed polarization is found to be due to the interstellar medium with average values of maximum polarization and wavelength corresponding to it as 1.55 per cent and 0.58 μm, respectively. This reveals a similar size distribution of dust grains to that in the general interstellar medium in the direction of NGC 2345. Alteration of dust properties near the distance of 1.2 kpc towards the direction of NGC 2345 has been noticed. The dust grains located beyond this distance are found to be aligned with the Galactic magnetic field, whereas a dispersion in orientation of the dust grains lying in the foreground of this distance is found. Polarizing efficiency of grains in this direction is found to be close to the average efficiency for our Galaxy. The decreased grain size along with the increased polarizing efficiency towards the core region of the cluster indicates the local radiation field is higher within the cluster which is responsible for the increased alignment efficiency of small grains. The wavelength of maximum polarization (associated with the average size of aligned grains) is also found to increase with extinction and reduces with the increase in polarizing efficiency, which can be explained by the radiative torque alignment mechanism.

Foreground Dust Properties toward the Cluster NGC 7380

“…3.8. The Variation of l max and Polarizing Efficiency There have been studies where l max is found to be weakly correlated with A V (e.g., Whittet et al 2001;Andersson & Potter 2007;Whittet et al 2008;Il'in et al 2018;Singh et al 2022). For our data sets, we found a Pearson correlation coefficient (r) between l max and A V of 0.23 with a probability of no correlation of 0.15, indicating that the relation is not statistically significant.…”

“…At higher extinction, the lower efficiency of polarization indicates that the alignment mechanism for grains is weaker in high-extinction regions. A power-law decay of polarizing efficiency with extinction is seen in various studies (Whittet et al 2001(Whittet et al , 2008Alves et al 2014;Andersson et al 2015;Hoang et al 2015;Jones et al 2015;Medan & Andersson 2019;Soam et al 2021;Singh et al 2022); therefore, we fitted the power law between these parameters, and the same is shown in log-log scale in Figure 6 ) was found to be followed in the region of the cluster NGC 7380. The efficiency of alignment in the region can be inferred from the value of the power-law exponent, e.g., an exponent of −1 shows negligible alignment efficiency.…”

“…In our studies (e.g., Singh et al 2022 for NGC 2345), we aim to probe dust properties and grain alignment physics by observing the polarization of starlight from open star clusters.…”

Exploring NGC 2345: A Comprehensive Study of a Young Open Cluster through Photometric and Kinematic Analysis

“…The 5 The cluster identification chart is taken from the Digitized Sky Survey (DSS) and shown in Figure 1. 6 The estimated distance, reddening (E(B − V )), and age of this cluster fall within the ranges of 2.2-3.0 kpc, 0.59-0.68 mag, and 55-79 Myr (Kharchenko et al 2005(Kharchenko et al , 2013Carraro et al 2014;Cantat-Gaudin et al 2018;Alonso-Santiago et al 2019;Singh et al 2022). Kharchenko et al (2005) derived the core and cluster radius as ¢ 4.2 and ¢ 7.2, respectively, whereas Alonso-Santiago et al (2019) estimated the core radius 3 44 ± 0 08, tidal radius 18 7 ± 1 2, and metallicity [Fe/H] = −0.28 for the cluster.…”