BVI Photometry and the Red Giant Branch Luminosity Function of M15

TL;DR

This study provides new $BVI$ photometry for M15, determining its age and distance, and finds good agreement between observed and modeled stellar luminosity functions, enhancing understanding of this globular cluster.

Contribution

It offers new photometric data and refined parameters for M15, with improved agreement between observed and theoretical luminosity functions.

Findings

Age of M15 estimated at 13.0 ± 1.0 Gyr

Distance modulus (m-M)_V = 15.4 ± 0.1

Good match between observed and modeled luminosity functions

Abstract

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.