Astron. Astrophys. Suppl. Ser. 144, 227-233

First results of a photometric and astrometric study of the globular cluster M 71 (NGC 6838)

M. Geffert^1,2 - G. Maintz¹

Send offprint request: M. Geffert

1 - Sternwarte der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
2 - Observatoire de Bordeaux, URA 352 CNRS/INSU, BP. 89, F-33270 Floirac, France

Received September 7, 1998; accepted March 7, 2000

Abstract:

We present the first results of a photometric and astrometric investigation of stars in the region of the globular cluster M 71 (NGC 6838). Using wide field CCD observations we determined B and V magnitudes of 4450 stars up to a limiting magnitude of V $\leq$ 18.5 mag. Relative proper motions were used to derive membership probabilities for stars with $R<3\hbox{$^\prime$ }$ around the centre of M 71. Our colour-magnitude diagram (CMD) of 320 probable cluster members reaches down to V = 18. A well defined red giant bump - for the first time seen in M 71 - could be detected in our CMD. From isochrone fitting we find M 71 metal poorer and older than previously assumed. Four faint variable stars were confirmed to be members of M 71. Moreover, we detected 13 blue stragglers among our cluster members.

Key words: astrometry -- (stars:) blue stragglers -- (Galaxy:) globular clusters: individual: M 71