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M 67

Odprta kopica - Open Cluster M67 (NGC 2682), type 'f', in cancer

Rektascenzija 08 : 50.4 (u:m)
Deklinacija +11 : 49 (sto:m)
Razdalja 2.7 (*1000 sv.l.)
Vizual. magnituda 6.1 (mag)
Zorni kot 30.0 (loc min)

M67 is one of the oldest known open clusters, and by far the oldest of Messier's open clusters, being aged at 3.2 billion years in the Star Catalog 2000; Mallas/Kreimer quote an even higher, but probably outdated value of 10 billion years. New estimates of G. Meynet's Geneva Team indicate an age of 4.0 billion years. Note: This is still less than the age of our Solar System, but open clusters usually get destructed much faster. It has been calculated that M67 can expect to exist as a cluster for about another 5 billion years.

Only few known open clusters were found to be older, among them probably NGC 188 at about 5 billion years, longly quoted as the oldest known cluster, and NGC 6791, which is about 7 billion years old (according to Götz), and is currently the oldest known open cluster in our Milky Way galaxy.

At this later stage of evolution, the open cluster M67 shows, in its Hertzsprung-Russell diagram, a well-developed red giant branch, while the main sequence ends to the hot blue end at spectral class A or F. It contains 11 bright K-type giants of absolute magnitude +0.5 to +1.5, and several stars scattered on the horizontal branch. However, it also contains some strange stars near the bluer main sequence, representatives of the so-called Blue Stragglers, the brightest of which is of spectral class B8 or B9 and apparent mag 10, corresponding to a luminosity of 50 times that of the Sun at the distance of M67 (2,700 light years according to Glyn Jones and Götz, 2600 from the Sky Catalog 2000). The total number of stars in M67 is probably at least about 500. The Trumpler type of this cluster is given as II,2,r (Trumpler according to Glyn Jones), II,2,m (Sky Catalog 2000) or II,3,r (Götz).

According to Cecilia Payne-Gaposhkin, M67 contains nearly 200 white dwarfs.

Povzeto po:
Hartmut Frommert (spider@seds.org)
Christine Kronberg (smil@lrz.uni-muenchen.de)

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