Photometry of Star Clusters in the M31 Galaxy. Aperture Size Effects

TL;DR

This paper investigates how aperture size influences star cluster photometry accuracy in crowded fields of the M31 galaxy, highlighting the importance of accounting for background crowding biases in color measurements.

Contribution

It presents an analysis of aperture effects on photometry of 285 star clusters in M31, emphasizing the need to correct for crowding biases before deriving cluster parameters.

Findings

Photometry errors generally reflect measurement accuracy for bright objects.

Color uncertainties for faint, crowded objects may be underestimated.

Comparison with HST data validates the photometry approach.

Abstract

A study of aperture size effects on star cluster photometry in crowded fields is presented. Tests were performed on a sample of 285 star cluster candidates in the South-West field of the M31 galaxy disk, measured in the Local Group Galaxy Survey mosaic images (Massey et al. 2006). In the majority of cases the derived UBVRI photometry errors represent the accuracy of cluster colors well, however, for faint objects, residing in crowded environments, uncertainties of colors could be underestimated. Therefore, prior to deriving cluster parameters via a comparison of measured colors with SSP models, biases of colors, arising due to background crowding, must be taken into account. A comparison of our photometry data with Hubble Space Telescope observations of the clusters by Krienke and Hodge (2007) is provided.