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Astron. Astrophys. 320, 776-782 (1997)

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Tidal radii of the globular clusters M 5, M 12, M 13, M 15, M 53, NGC 5053 and NGC 5466 from automated star counts

I. Lehmann 1 and R.-D. Scholz 2

1 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
2 WIP Astronomie / Universität Potsdam, Sternwarte Babelsberg, D-14482 Potsdam, Germany

Received 12 August 1996 / Accepted 9 October 1996


We present new tidal radii for seven Galactic globular clusters using the method of automated star counts on Schmidt plates of the Tautenburg, Palomar and UK telescopes. The plates were fully scanned with the APM system in Cambridge (UK). Special account was given to a reliable background subtraction and the correction of crowding effects in the central cluster region. For the latter we used a new kind of crowding correction based on a statistical approach to the distribution of stellar images and the luminosity function of the cluster stars in the uncrowded area. The star counts were correlated with surface brightness profiles of different authors to obtain complete projected density profiles of the globular clusters. Fitting an empirical density law (King 1962) we derived the following structural parameters: tidal radius [FORMULA], core radius [FORMULA] and concentration parameter c. In the cases of NGC  5466, M 5, M 12, M 13 and M 15 we found an indication for a tidal tail around these objects (cf. Grillmair et al. 1995).

Key words: globular clusters: general – methods: statistical

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998