|Authors||S. Meibom(1,2), J. Andersen(3), B. Nordström(3)|
(1) Astronomical Observatory, Copenhagen, Denmark
(2)Astronomy Department, University of Wisconsin, Madison, USA
(3) Astronomical Observatory, Copenhagen, Denmark
(4) Lund Observatory, Lund, Sweden
|Submitted to||Astronomy & Astrophysics|
|Links||IC 4651 / NGC 3680|
Including the ~650 stars newly discovered from the photometry, we estimate the present total mass of IC 4651 to be ~630 M_sun excluding any undetected stellar remnants. The corresponding tidal cutoff radius is ~22'. IC 4651 shows evidence of moderate mass segregation: Most of the turn-off stars and nearly all the red giants are located at radii smaller than ~7', while the lower main-sequence stars are less centrally concentrated. The spatial distributions of cluster and field stars indicate that additional cluster stars are probably still to be found outside the fields studied so far. Comparison of the present mass function of IC 4651 with plausible initial mass functions indicates that the cluster initially contained at least ~8300$ stars with a total mass of ~5300 M_sun. Thus, of the original cluster stars only ~7%, containing ~12% of the initial mass, remain today. Of the initial cluster mass, ~35% has been lost due to evolution of the most massive stars into white dwarfs or other remnants while the remaining ~53%, comprising ~93% of the original low-mass stars, appear to have migrated out of the observed field or been lost from the cluster altogether. IC 4651 is currently 1 kpc closer to the Galactic center than its ``sister'' cluster NGC 3680 (Nordström et al. 1997), but their Galactic orbital parameters indicate that the mean orbital radius of IC4651 is in fact larger by 0.7 kpc, providing a plausible reason why it is much less advanced in its dynamical evolution than the coeval cluster NGC 3680.