Deriving physical parameters of unresolved star clusters

VII. Adaptive aperture photometry of the M 31 PHAT star clusters^★

Center for Physical Sciences and Technology, Saulėtekio av. 3, 10257 Vilnius, Lithuania
e-mail: rima.stonkute@ftmc.lt; vladas.vansevicius@ftmc.lt

Received: 9 June 2023
Accepted: 20 July 2023

Abstract

Context. 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.

Aims. In this study, we aim to supplement the homogeneous multi-colour aperture photometry results published in Paper I and provide a complete M 31 Panchromatic Hubble Andromeda Treasury (PHAT) survey star cluster photometry catalogue for further analysis.

Methods. 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.

Results. We present the second part of the star cluster aperture photometry catalogues for a sample of 1477 star clusters from the M 31 PHAT survey not covered in Paper I. Compared to the M 31 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.