SCYON Abstract

Received on July 13 2004

Systematic uncertainties in the analysis of star cluster parameters based on broad-band imaging observations

AuthorsR. de Grijs1, P. Anders2, H. J. G. L. M. Lamers3,4, N. Bastian3,5, U. Fritze-v. Alvensleben2, G. Parmentier6,7, M. E. Sharina8,9, and S. Yi10
Affiliation1 Department of Physics & Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK;
2 Universitätssternwarte, University of Göttingen, Geismarlandstr. 11, 37083 Göttingen, Germany;
3 Astronomical Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands;
4 SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands;
5 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany;
6 Institute of Astrophysics and Geophysics, Université de Liège, Sart-Tilman (B5c), 4000 Liège, Belgium;
7 Astronomical Institute, University of Basel, Venusstrasse 7, CH-4102 Binningen, Switzerland;
8 Special Astrophysical Observatory, Russian Academy of Science, N. Arkhyz, KChR, 369167, Russia;
9 Isaac Newton Institute, Chile, SAO Branch;
10 Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
Submitted toMonthly Notices of the Royal Astronomical Society


High-resolution Hubble Space Telescope (HST) imaging observations of star cluster systems provide a very interesting and useful alternative for stellar population analyses to spectroscopic studies with 8m-class telescopes; the latter become prohibitive for large cluster samples. Here, we assess the systematic uncertainties in (young) cluster age, mass, and - to a lesser extent - extinction and metallicity determinations, based on broad-band imaging observations with the HST. Any significant differences among the resulting parameters are due to the details of the various, independently developed modelling techniques used, rather than to the stellar population models themselves. Despite the model uncertainties and the selection effects inherent to most methods used, we find that the relative age and mass distributions of a given young (~ 109 yr) cluster system can be derived fairly robustly and consistently. The relative mass distributions can be obtained with a higher degree of confidence than the relative age distributions, although the key features (i.e., clear peaks in the age distribution) remain reproducible. We argue that as extensive a wavelength coverage as possible is required to obtain robust and internally consistent age and mass estimates for the individual objects, with reasonable uncertainties. Finally, we conclude that one should ideally compare one's original photometry with cluster models calculated for the actual filter system used for the observations, to reduce the modelling uncertainties.