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Globular Cluster M 71 (NGC 6838)

Date:22./23.10.1995 (B&I/V) Time:20:25 UT (B,I), 21:05 UT (V) Exposure:B:42m, V:20m, I:9m
Field of View:20.7' x 18.8' Receiver: WWFPP, 20482 CCD Filter:B, V, I
Instrument: 1.23m Observatory: Calar Alto Observer:T. Credner, S. Kohle

© Copyright by the observers

Astronomical Institutes of the University of Bonn

From Colors to Astrophysics

This three color composite is consisting of Johnson B, V, and I filter exposures, represented in blue, green, and red respectively.

M 71 is a rich but relativ small star cluster lying in the Milky Way of the constellation Sagitta. Its classification, whether to be of globular or open cluster type, was a long debate. In comparison with usual globular clusters like M 10, its star distribution is very loose but on the other hand the cluster is much more rich and condensed than typical open clusters like NGC 2194. The old age of 15 Gyrs is typical for galactic globular clusters, but the abundance of heavy elements (metallicity) is as high as in galactic plane objects like open clusters. And the clusters orbit is also more like the one of open clusters inside our galactic plane.
Finally, Zinn (1985) introduced an intermediate class of globular clusters that belong to the galactic plane population and not as usual to the spherical distributed halo population. M 71 and also 47 Tucanae would belong to this new class.

See also:

  • Color-magnitude diagram of M 71 by Hodder et al. 1992
  • Catalogue of Milky Way Globular Cluster Parameters by William E. Harris
  • SEDS infos