Journal Article

An assessment of broad-band optical colours as age indicators for star clusters

M. Hancock, B. J. Smith, M. L. Giroux and C. Struck

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 389, issue 3, pages 1470-1478
Published in print September 2008 | ISSN: 0035-8711
Published online September 2008 | e-ISSN: 1365-2966 | DOI:
An assessment of broad-band optical colours as age indicators for star clusters

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We present an empirical assessment of the use of broad-band optical colours as age indicators for unresolved extragalactic clusters and investigate stochastic sampling effects on integrated colours. We use the integrated properties of Galactic open clusters (OCs) as models for unresolved extragalactic clusters. The population synthesis code Starburst99 (SB99) and four optical colours were used to estimate how well we can recover the ages of 62 well-studied Galactic OCs with published ages. We provide a method for estimating the ages of unresolved clusters and for reliably determining the uncertainties in the age estimates. Our results support earlier conclusions based on comparisons to synthetic clusters, namely the (UB) colour is critical to the estimation of the ages of star-forming regions. We compare the observed optical colours with those obtained from SB99 using the published ages and get good agreement. The scatter in the (BV)observed− (BV)model is larger for lower luminosity clusters, perhaps due to stochastic effects.

Keywords: methods: data analysis; open clusters and associations: general; galaxies: star clusters; galaxies: stellar content

Journal Article.  6196 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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