BVI Photometry and the Red Giant Branch Luminosity Function of M15
  We present new $BVI$ photometry containing 40,000 stars of the Galactic globular cluster M15 (NGC 7078) covering a $25 \times 25$ arcminute area centered on the cluster with a magnitude range from the tip of the Red Giant Branch to three magnitudes below the main sequence turn-off. Using $\alpha$-enhanced Dartmouth Stellar Evolution Program models, we find an age of $13.0 \ \pm \ 1.0$ Gyr and distance modulus of $(m-M)_V = 15.4 \pm 0.1$ through isochrone fitting. Unlike previous works, we find good agreement between the observed completeness-corrected stellar luminosity function and models. 
Diane K. Feuillet, Nathaniel E. Q. Paust, and Brian Chaboyer
astro-ph.SR astro-ph.GA