Hubble Space Telescope Observations of Galactic Globular Cluster Cores. I. NGC 6362 and NGC 6934

We present observations of the centers of the Galactic globular clusters NGC 6362 and NGC 6934 obtained with the Hubble Space Telescope/Wide Field Planetary Camera 2 as part of the snapshot program GO-7470. The B, V color-magnitude diagrams (CMDs) are presented for 4104 stars in NGC 6362 and for 8187 stars in NGC 6934. From the CMDs, we obtain (m - M)V = 14.67 ± 0.20 and E(B-V) = 0.06 ± 0.03 for NGC 6362 and (m - M)V = 16.37 ± 0.20 and E(B-V) = 0.05 ± 0.02 for NGC 6934. Each cluster shows a well-defined sequence of blue stragglers. Both the CMD and the luminosity function (LF) of the blue stragglers differ in the two clusters, suggesting two different origins for these stars. NGC 6362 has a strikingly narrow blue straggler sequence. The data have also been used to derive a complete LF, which extends from the red giant branch tip to 2–3 mag below the turnoff. In the case of NGC 6362, which has the deepest LF, the theoretical LF cannot match both the evolved LF and that of the main sequence with any reasonable mass-function slope. The LF has also been used to estimate the ages of the two clusters. A comparison with the theoretical LF, the more classical isochrone fitting, and the ΔV suggest an age between 13 and 16 Gyr for both clusters. No significant age difference between NGC 6362 and NGC 6934 is observed