The red giant branch BVI luminosity function of M15
We present new BVI observations of the Galactic globular cluster M15. The observations cover an area 25 arcminutes square centered on the cluster. The color-magnitude diagram contains over 40,000 stars and extensive artificial star tests were performed to produce luminosity functions. The data extends from the tip of the red giant branch to below the main sequence turnoff. We compare the color-magnitude diagrams and RGB luminosity functions to Dartmouth Stellar Evolution Program (DSEP) models. Using an alpha abundance of [α/Fe] = 0.2 and a metallicity of [Fe/H] = −2.10 we find an age of 14.0 ± 1.0 Gyr and distance modulus of (m−M)v̳ = 15.3 ± 0.1 through isochrone fitting. We find good agreement between the CMD fit and the fit to the luminosity functions.
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