High Angular Resolution [ITAL]JHK[/ITAL] Imaging of the Centers of the Metal-poor Globular Clusters NGC 5272 (M3), NGC 6205 (M13), NGC 6287, and NGC 6341 (M92)

The Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) hasbeen used to obtain high angular resolution JHK images of the centers of themetal-poor globular clusters NGC5272 (M3), NGC6205 (M13), NGC6287, and NGC6341(M92). The color-magnitude diagrams (CMDs) derived from these data include theupper main sequence and most of the red giant branch (RGB), and the clustersequences agree with published photometric measurements of bright stars inthese clusters. The photometric accuracy is limited by PSF variations, whichintroduce systematic errors of a few hundredths of a magnitude near the AOreference star. The clusters are paired according to metallicity, and the near-infrared CMDsand luminosity functions are used to investigate the relative ages within eachpair. The near-infrared CMDs provide the tightest constraints on the relativeages of the classical second parameter pair NGC5272 and NGC6205, and indicatethat these clusters have ages that differ by no more than +/- 1 Gyr. Theseresults thus support the notion that age is not the second parameter. Wetentatively conclude that NGC6287 and NGC6341 have ages that differ by no morethan +/- 2 Gyr. However, the near-infrared spectral energy distributions ofstars in NGC6287 appear to differ from those of stars in outer halo clusters,bringing into question the validity of this age estimate.Comment: 22 pages, 17 figures. To be published in the Astronomical Journa