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Astron. Astrophys. 324, 915-928


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HST observations of blue Straggler stars in the core
of the globular cluster M 3*

F.R. Ferraro1, B. Paltrinieri1, F. Fusi Pecci1,2, C. Cacciari1,3, B. Dorman4,5, R.T. Rood5, R. Buonanno6, C.E. Corsi6, D. Burgarella7, and M. Laget7

1 Osservatorio Astronomico di Bologna, Via Zamboni 33, I-40126 Bologna, Italy
2 Stazione Astronomica di Cagliari, I-09012 Capoterra, Italy
3 Space Telescope Science Institute, Baltimore, USA
4 Goddard Space Flight Center, NASA Greenbelt, USA
5 University of Virginia, Charlottesville, USA
6 Osservatorio Astronomico di Roma, Roma, Italy
7 Laboratoire d'Astronomie Spatiale, CNRS Marseille, France

Received 17 December 1996 / Accepted 17 February 1997

Abstract

The core of the Galactic Globular Cluster M 3 (NGC 5272) has been observed with the WFPC2 through the filters F255W, F336W, F555W, and F814W. Using these observations along with a thorough reanalysis of earlier catalogs, we have produced a catalog of blue straggler stars (BSS) spanning the cluster. Earlier studies and the fainter part of our sample suffer severe selection biases. Our analysis is based on a more reliable bright global sample of 122 BSS. We confirm earlier suggestions that the radial BSS distribution in M 3 is bimodal. It is strongly peaked in the center, has a clear dip 100-200 FORMULA from the center, and rises again at larger radii. The observed distribution agrees with the dynamical model of Sigurdsson et al. (1994) which takes into account both star collisions and merging of primordial binaries for the origin of BSS. The observed luminosity functions of BSS in the inner and outer parts of the cluster are different. Interpreting these using the models of Bailyn & Pinsonneault (1995), we suggest that the BSS in the inner cluster are formed by stellar collisions and those in the outer cluster from merging primordial binaries.

Key words: globular clusters: individual: M 3 - stars: population II - stars: Blue Stragglers

Send offprint requests to: F.R. Ferraro, ferraro@astbo3.bo.astro.it
*Tables 2,3 and 4 are available in electronic form only via anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html


© European Southern Observatory (ESO) 1997

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