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B.J. Anthony-Twarog, B.A. Twarog, M.M. Cracraft, D. Tanner, L. Mayer (Univ. of Kansas)
As part of an ongoing program to refine the fundamental characteristics of open clusters for use in studying stellar and galactic evolution, CCD intermediate and narrow-band photometry has been obtained of the northern old open clusters NGC 2420 and NGC 6791 using the 0.9m WIYN telescope at KPNO. For NGC 2420, the critical question is the cluster metallicity. Long considered to be moderately metal-poor relative to the sun ([Fe/H] ~-0.4), recent photometric observations have claimed a solar abundance for the object. By isolating likely cluster members using a combination of spatial distribution and photometric indices, a sample of over 100 highly probable members with high precision photometry near the cluster turnoff has been generated. From H\beta photometric analysis, the cluster reddening is well defined at E(B-V) = 0.054, with a standard error of the mean of 0.004 mag. Adopting this reddening, one can derive metallicity from both the m1 and hk indices, leading to a weighted average of [Fe/H] = -0.35 with an uncertainty < 0.05 dex. These values are totally consistent with previous cluster studies and exclude the possibility that NGC 2420 has solar metallicity. Similar analysis is underway for NGC 6791 and will be reported on at the meeting.
We acknowledge the generosity of the University of Kansas General Research Fund and the WIYN Open Cluster Survey consortium.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.