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Astron. Astrophys. 319, 45-51 (1997)

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The true shapes of the globular clusters in M 31

P.V. Baev 1, N. Spassova 1 and A. Staneva 2

1 Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko chauss [FORMULA] e, BG-1784 Sofia, Bulgaria
2 Department of Astronomy, Faculty of Physics, St. Kliment Okhridski University of Sofia, 5 James Bourchier street, BG-1126 Sofia, Bulgaria

Received 24 April 1996 / Accepted 2 August 1996


The true shapes of the globular clusters (GCs) in M 31 have been derived from observed ellipticities. The nonparametric kernel estimates for the axis ratios distributions in the case of oblate or prolate spheroid hypothesis and the parametric estimates in the case of triaxial ellipsoid hypothesis have been used. The cluster shapes are inconsistent with the oblate/prolate hypothesis and only the shapes of the GCs situated beyond the outermost visible limit of M 31 disk (so called "halo" clusters) are consistent with that hypothesis. We conclude that the GCs in the M 31 are most likely triaxial ellipsoids. The distributions of intrinsic axis ratios derived on the base of triaxial ellipsoid hypothesis have been compared with results published earlier. It has been found out that the clusters in M 31 are more spherical than those in the LMC and in the SMC while the GCs in the Galaxy are rounder than those in M 31.

Key words: globular clusters: general – galaxies: individual: M 31 – galaxies: star clusters

Send offprint requests to: P.V. Baev (baers@ms3.tu-varna.acad.bg)

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998