Deriving physical parameters of unresolved star clusters. VII. Adaptive aperture photometry of the M31 PHAT star clusters

TL;DR

This paper enhances star cluster photometry in M31 by providing a comprehensive catalogue using adaptive aperture techniques to improve accuracy in unresolved cluster analysis.

Contribution

It offers a complete, homogeneous photometry catalogue for 1477 M31 star clusters using adaptive aperture methods, supplementing previous data and refining measurement techniques.

Findings

Improved color index consistency with adaptive apertures.

Enhanced photometry catalogue for M31 star clusters.

Refined aperture and background measurement methods.

Abstract

This work is the seventh study in a series dedicated to investigating degeneracies of simultaneous age, mass, extinction, and metallicity determinations of partially resolved or unresolved star clusters with Hubble Space Telescope broadband aperture photometry. In the sixth work (hereafter, Paper I), it was demonstrated that the adaptive aperture photometry, performed to avoid the majority of the projected foreground and background stars falling within the apertures, gives more consistent colour indices for star clusters. In this study, we aim to supplement the homogeneous multi-colour aperture photometry results published in Paper~I and provide a complete M31 Panchromatic Hubble Andromeda Treasury (PHAT) survey star cluster photometry catalogue for further analysis. Following Paper I, we used a two-aperture approach for photometry. The first aperture is the standard one used to measure total cluster fluxes. The second (smaller) aperture is introduced to avoid the bright foreground and background stars projecting onto the clusters. We selected the radii of smaller apertures to be larger than the half-light radii of the clusters. We present the second part of the star cluster aperture photometry catalogues for a sample of 1477 star clusters from the M31 PHAT survey not covered in Paper I. Compared to the M31 PHAT star cluster aperture photometry catalogue published by Johnson et al., adjustments were made to the cluster centre coordinates, aperture sizes, and sky background levels.