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L. Trouille, B. Chaboyer (Dartmouth College, Physics and Astronomy Department)
Palomar 13 offers the chance to study a paradigm case of a ‘young halo’ globular cluster with its second-parameter effect horizontal branch morphology, mean retrograde rotation, relatively eccentric orbits, and high Zmax values. Recent studies by Siegel et al. (2001, AJ, 121, 935) and Cote et al. (2002, ApJ, 574, 783) suggest that the cluster is in its final throes of destruction as it undergoes catastrophic heating during its recent perigalacticon passage. In order to further explore the intricacies of Palomar 13, we must accurately determine its age. The cluster was observed in BVI using the 2.4m Hiltner Telescope at the MDM observatory. The resulting color-magnitude diagram includes 697 stars and exhibits fairly well-defined upper main sequence, main sequence turn-off, and subgiant branches. In conjunction with previous studies, the horizontal branch is extremely poor and the redgiant branch is relatively sparse. Palomar 13 is found to have ten centrally located blue stragglers and four RR Lyrae stars. The age was determined using isochrone fitting and the more robust method of using the difference in magnitude between the subgiant branch (0.05 magnitude redder than the turnoff) and the horizontal branch. We find the age of Palomar 13 to be 10.5 +/- 1.0 Gyr, which suggests that Palomar 13 may be younger by 1 or 2 Gyr compared to globular clusters of similar composition.
The author(s) of this abstract have provided an email address for comments about the abstract: Laura.Trouille@Dartmouth.Edu
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.