Astron. Astrophys. 324, 505-522 (1997)

Core velocity dispersions for 25 Galactic and 10 old Magellanic globular clusters ^{* **}

Pierre Dubath ^{1, 2}, Georges Meylan ³ and Michel Mayor <sup>1

1</sup> Observatoire de Genève, ch. des Maillettes 51, CH-1290 Sauverny, Switzerland
² INTEGRAL Science Data Centre, ch. d'Écogia 16, CH-1290 Versoix, Switzerland
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching, Germany

Received 30 July 1996 / Accepted 13 September 1996

Abstract

We present, for 25 Galactic and 10 old Magellanic globular clusters, projected velocity dispersion () measurements obtained by applying a cross-correlation technique to integrated-light spectra. In order to understand and estimate the statistical errors of these measurements due to small numbers of bright stars dominating the integrated light, we provide an extensive discussion based on detailed numerical simulations. These errors are smaller if the integration area is larger and/or the cluster concentration higher. The simulations show that measurements are reliable when the integrated light within the integration area is brighter than a given magnitude. The statistical errors on the measurements of Magellanic globular clusters are small because of a physically large integration area, whereas they can be important for measurements carried out over small central areas in Galactic clusters. The present observational results are used to outline a few characteristics of the globular cluster fundamental plane. In this respect, the old Magellanic globular clusters appear similar to the Galactic clusters.

Key words: (Galaxy:) globular clusters: general stars: kinematics techniques: radial velocities galaxies: star clusters Magellanic Clouds

* Based on observations collected at the European Southern Observatory, La Silla, Chile
** Tables 6 and 7 are also available electronically at the CDS via anonymous ftp 130.79.1285 or via http://cdsweb.v.strasbg.fr/Abstract.html

Send offprint requests to: Pierre.Dubath@obs.unige.ch

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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