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Post Info TOPIC: Old Galactic open clusters
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RE: Old Galactic open clusters
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Title: Five old open clusters more in the outer Galactic disk
Authors: Giovanni Carraro (ESO-Chile), Yuri Beletsky (LCO), Gianni Marconi (ESO-Chile)

New photometric material is presented for 6 outer disk supposedly old, Galactic star clusters: Berkeley 76, Haffner 4, Ruprecht 10, Haffner 7, Haffner 11, and Haffner 15, that are projected against the rich and complex Canis Major overdensity at 225° \leq l \leq 248° , -7° \leq b \leq -2°. This CCD data-set, in the UBVI pass-bands, is used to derive their fundamental parameters, in particular age and distance. Four of the program clusters turn out to be older than 1 Gyr. This fact makes them ideal targets for future spectroscopic campaigns aiming at deriving their metal abundances. This, in turn, contributes to increase the number of well-studied outer disk old open clusters. Only Haffner 15, previously considered an old cluster, is found to be a young, significantly reddened cluster, member of the Perseus arm in the third Galactic quadrant. As for Haffner~4, we suggest an age of about half a Gyr. The most interesting result we found is that Berkeley~76 is probably located at more than 17 kpc from the Galactic center, and therefore is among the most peripherical old open clusters so far detected. Besides, for Ruprecht~10 and Haffner~7, which were never studied before, we propose ages larger than 1 Gyr. All the old clusters of this sample are scarcely populated and show evidence of tidal interaction with the Milky Way, and are therefore most probably in advanced st ages of dynamical dissolution.

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Blobrana


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Posts: 131433
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Title: The old Galactic open clusters FSR1716 and Czernik23
Authors: Charles Bonatto, Eduardo Bica

Open clusters older than ~ 4 Gyr are rare in the Galaxy. Affected by a series of mass-decreasing processes, the stellar content of most open clusters dissolves into the field in a time-scale shorter than ~1 Gyr. In this sense, improving the statistics of old objects may provide constraints for a better understanding of the dynamical dissolution of open clusters. Isochrone fits indicate that FSR 1716 is more probably an old (~7 Gyr) and absorbed (\aV=6.3±0.2) open cluster, located ~0.6 kpc inside the Solar circle in a contaminated central field. However, we cannot rule out the possibility of a low-mass, loose globular cluster. Czernik 23 is shown to be an almost absorption-free open cluster, ~5 Gyr old, located about 2.5 kpc towards the anti-centre. In both cases, Solar and sub-Solar ([Fe/H] ~ -0.5) metallicity isochrones represent equally well the stellar sequences. Both star clusters have a low mass content (\la200 \ms) presently stored in stars. Their relatively small core and cluster radii are comparable to those of other open clusters of similar age. These structural parameters are probably consequence of the several Gyrs of mass loss due to stellar evolution, tidal interactions with the disk (and bulge in the case of FSR 1716), and possibly giant molecular clouds. Czernik 23, and especially FSR 1716, are rare examples of extreme dynamical survivors. The identification of both as such represents an increase of ~10% to the known population of open clusters older than ~4 Gyr in the Galaxy.

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