Deriving structural parameters of semi-resolved star clusters. FitClust: a program for crowded fields

Abstract

Context. An automatic tool to derive structural parameters of semi-resolved star clusters located in crowded stellar fields in nearby galaxies is needed for homogeneous processing of archival frames. Aims. We have developed a program that automatically derives the structural parameters of star clusters and estimates errors by accounting for individual stars and variable sky background. Methods. Models of observed frames consist of the cluster's surface brightness distribution, convolved with a point spread function; the stars, represented by the same point spread function; and a smoothly variable sky background. The cluster's model is fitted within a large radius by using the Levenberg-Marquardt and Markov chain Monte Carlo algorithms to derive structural parameters, the flux of the cluster, and individual fluxes of all well-resolved stars. Results. FitClust, a program to derive structural parameters of semi-resolved clusters in crowded stellar fields, was developed and is available for free use. The program was tested on simulated cluster frames, and was used to measure clusters of the M31 galaxy in Subaru Suprime-Cam frames. Conclusions. Accounting for bright resolved stars and variable sky background significantly improves the accuracy of derived structural parameters of star clusters. However, their uncertainty remains dominated by the stochastic noise of unresolved stars.

10 pages, 9 figures, typo correction

References in corpus (9)

• Structural parameters for globular clusters in M31 and generalizations for the fundamental plane
• Luminosity profiles and sizes of massive star clusters in NGC 7252
• An extended star cluster at the outer edge of the spiral galaxy M33
• Probabilistic Catalogs for Crowded Stellar Fields
• Deriving physical parameters of unresolved star clusters. I. Age, mass, and extinction degeneracies
• The Panchromatic Hubble Andromeda Treasury III. Measuring Ages and Masses of Partially Resolved Stellar Clusters
• A Survey of Star Clusters in the M31 South-West Field. UBVRI Photometry and Multi-Band Maps
• Newly Identified Star Clusters in M33. III. Structural Parameters
• Photometry of Star Clusters in the M31 Galaxy. Aperture Size Effects

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