Search and analysis of blue straggler stars in open clusters

¹ Dipartimento di Astronomia, Università di Padova, vicolo dell'Osservatorio 2, Padova 35122, Italy e-mail: demarchi-piotto@pd.astro.it
² Institue of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 OHA, UK e-mail: fda@ast.cam.ac.uk
³ Andes Fellow, Departamento de Astronómia, Universidad de Cile, Casilla 36-D, Santiago, Chile
⁴ Astronomy Department, Yale University, PO Box 208101 New Haven, CT 06520-8101, USA e-mail: gcarraro@das.uchile.cl
⁵ Lund Observatory, Box 43, 221 00 Lund, Sweden e-mail: mbd@astro.lu.se

Received: 23 January 2006
Accepted: 14 July 2006

Abstract

Aims.This paper presents a new homogeneous catalogue of blue straggler stars (BSS) in Galactic open clusters.

Methods.Photometric data for 216 clusters were collected from the literature and 2782 BSS candidates were extracted from 76 of them.

Results.We found that the anticorrelation of BSS frequency vs. total magnitude identified in similar studies conducted on Galactic globular clusters extends to the open cluster regime: clusters with smaller total magnitude tend to have higher BSS frequencies. Moreover, a clear correlation between the BSS frequency (obtained normalising the total number of BSS either to the total cluster mass or, for the older clusters, to the total number of clump stars) and the age of the clusters was found. A simple model is developed here to try to explain this last and new result. The model allows us to ascertain the important effect played by mass loss in the evolution of open clusters.