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P. Mallik (University of Oregon), J. Christensen, A. Saha (NOAO)
We present new time sequence photometry of the globular cluster M3 in the extended Thuan-Gunn uvgri system obtained over 5 consecutive nights at KPNO. The data provide light curves of approximately 200 RR Lyrae stars in M3 in all 5 passbands. This system, which measures the Balmer jump, provides both temperature and surface gravity and is particularly suited for Baade-Wesselink studies for finding absolute visual magnitudes of these variables. Spectroscopy of 29 RR Lyrae stars with the multi-object HYDRA spectrograph on WIYN provides velocity curves of the RR Lyraes. Comparison with the mean cluster velocity for this ensemble removes systematic uncertainties in the center of mass velocity, which is the chief culprit in determining reliable abolute magnitudes. The independent measurement of RR Lyrae luminosities in a globular cluster is relevant to the estimation of ages of the oldest known stars, which in turn is of cosmological interest.
This research is supported in part by the Kitt Peak National Observatory site program of the Research Experience for Undergraduates, funded by the National Science Foundation.