Detailed study of B037 based on {\sl HST} images

TL;DR

This study uses HST images to analyze the structure, dust features, and photometric properties of the luminous, highly reddened M31 cluster B037, revealing a dust lane likely unrelated to the cluster's low metallicity.

Contribution

It provides detailed structural parameters and photometric analysis of B037, including the discovery of a dust lane and its implications, which were not previously characterized.

Findings

B037 contains a dust lane not from M31 or the Milky Way.

Structural parameters of B037 are precisely measured using King model fitting.

The dust lane's origin remains uncertain due to the cluster's low metallicity.

Abstract

B037 is of interest because it is both the most luminous and the most highly reddened cluster known in M31. Images of deep observations and of highly spatial resolutions with the Advanced Camera for Surveys on the {\sl HST} firstly show that this cluster is crossed by a dust lane. Photometric data in the F606W and F814W filters obtained in this paper provide that, colors of ($\rm {F606W-F814W}$) in the dust lane are redder $\sim 0.4$ mags than ones in the other regions of B037. The {\sl HST} images show that, this dust lane seems to be contained in B037, not from the M31 disk or the Milky Way. As we know, the formation of dust requires gas with a rather high metallicity. However, B037 has a low metallicity to be $\rm [Fe/H]=-1.07\pm 0.20$. So, it seems improbable that the observed dust lane is physically associated with B037. It is clear that the origin of this dust lane is worthy of future study. In addition, based on these images, we present the precise variation of ellipticity and position angle, and of surface brightness profile, and determine the structural parameters of B037 by fitting a single-mass isotropic King model. In the F606W filter, we derive the best-fitting scale radius, $r_0=0.56\pm0.02\arcsec~(=2.16\pm0.08~\rm{pc})$, a tidal radius, $r_t=8.6\pm0.4\arcsec~(=33.1\pm1.5~\rm{pc})$, and a concentration index $c=\log (r_t/r_0)=1.19\pm0.02$. In the F814W filter, we derive $r_0=0.56\pm0.01\arcsec~(=2.16\pm0.04~\rm{pc})$, $r_t=8.9\pm0.3\arcsec~(=34.3\pm1.2~\rm{pc})$, and $c=\log (r_t/r_0)=1.20\pm0.01$. The extinction-corrected central surface brightness is $\mu_0=13.53\pm 0.03~{\rm mag~arcsec^{-2}}$ in the F606W filter, and $12.85\pm 0.03~{\rm mag~arcsec^{-2}}$ in the F814W filter, respectively.