The age of NGC 6426, a metal-poor globular cluster in the galactic halo

We present B, V, R, and I photometry of the metal-poor globular cluster in the galactic halo, NGC 6426. The observations were performed using the 1.3 m Telescope at Skinakas Observatory in Crete. We derived the reddening of the cluster to be E(B - V)= 0.39 +/- 0.02 [E(V - I) = 0.53 +/- 0.03]. The metal abundance of the cluster was estimated from the shape of the red giant branch following the techniques by Sarajedini and by Da Costa & Armandroff. It was found to be [Fe/H] = -2.33 +/- 0.15 dex. The mean V magnitude of the RR Lyrae variables found in the cluster is 18.14 +/- 0.02 (based on a paper in preparation). The resulting distance modulus of the cluster is 16.41 +/- 0.07. Finally, we derived the relative age of NGC 6426. Using the methodology of Harris et al., we found that NGC 6426 is marginally older than M92 (by similar or equal to 0.7 Gyr). Following the Chaboyer, Demarque, & Sarajedini method we found NGC 6426 to have the same age as the mean metal-poor globular cluster of the galactic halo.