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Old Open Clusters in the Solar Neighbourhood

Stefan Schmeja
Zentrum fŁr Astronomie der Universitšt Heidelberg

There is a striking lack of old (t > 1 Gyr) open clusters in the solar neighbourhood (d < 1 kpc). Old open clusters show a larger scale height, so in combination with their small distance they may also lie at higher Galactic latitudes, whereas most systematic open cluster searches have been restricted to areas around the Galactic plane, and having a large angular extent, they do not stand out prominently as overdensities from the field. These are probably the reasons why those clusters have escaped detection so far. Our systematic search for stellar density enhancements using a star count algorithm on the 2MASS point source catalogue at Galactic latitudes |b| > 20° resulted in the discovery of 137 new open clusters with ages between 0.2 and 5 Gyr and distances < 3 kpc. Nevertheless, the volume < 1 kpc is still expected to contain about 60 unknown old clusters that probably have escaped our search.

2014 May 08, 13:30

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