International Journal of Astronomy and Astrophysics

Volume 2, Issue 3 (September 2012)

ISSN Print: 2161-4717   ISSN Online: 2161-4725

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Examining the M67 Classification as an Open Cluster

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DOI: 10.4236/ijaa.2012.23020    4,816 Downloads   8,145 Views  Citations


The cluster M67 (= NGC 2682) in Cancer is a rich stellar cluster, usually classified as an open cluster. Using our own observations with the 0.4 m telescope, we show that M67 is a tight group of about 1200 stars. The actual radius of the cluster is about 3.1 pc and the average mass of a star in the system is about . We also show that the ratio of the mean kinetic energy of the cluster to its mean gravitational potential energy , while the value predicted by the virial theorem is equal to . So the system is a gravitationally bound. This value of is considered as an evidence of quasi-stability of the cluster and allows us to use the Chandrasekhar-Spitzer relaxation time for M67 Myr as a characteristic dynamical relaxation time of the system. As the cluster is almost twice older its half-life time , it is argued that M67 was in the past (about 4 Gyr ago, close to its forma-tion) a relatively small ( stars) globular cluster, but got “open cluster” shape due to the dynamical evapora-tion of the majority of its stars.

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S. Naim and E. Griv, "Examining the M67 Classification as an Open Cluster," International Journal of Astronomy and Astrophysics, Vol. 2 No. 3, 2012, pp. 167-173. doi: 10.4236/ijaa.2012.23020.

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