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تسجيل مستخدم جديدA Precision Age Determination Technique for Globular Clusters
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Brian Chaboyer
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Globular cluster age estimates based on the absolute magnitude of the main sequence turn-off (mvto) are generally considered to be the most reliable from a theoretical viewpoint. However, the difficulty in determining mvto in observed colour-magnitude diagrams leads to a large error in the derived age. In this paper, we advocate the use of the absolute magnitude of the point which is brighter than the turn-off and 0.05 mag redder (mvb) as a precision age indicator. It is easy to measure this point on observed colour-magnitude diagrams, leading to small observational error bars. Furthermore, an extensive Monte Carlo calculation indicates that the theoretical uncertainty in mvb is similar to mvto. As a result, ages derived using mvb are at least a factor of 2 more precise than those derived using mvto. This technique is applied to the globular cluster M68 and an age of $12.8pm 0.3,$Gyr is derived (assuming $mvrr = 0.20,feh + 0.98$), indicating that M68 is a `young globular cluster. A homogeneous set of globular cluster age estimates with this precision would provide unprecedented insight into the formation of the Galactic halo.
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