Paxton, B., Smolec, R., Gautschy, A., Bildsten, L., Cantiello, M., Dotter, A., ... & Marchant, P. (2019). Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation. arXiv preprint arXiv:1903.01426.  
Salaris, M., Degl'Innocenti, S., & Weiss, A. (1997). The age of the oldest globular clusters. Retrieved from https://iopscience.iop.org/article/10.1086/303909/fulltext/34870.text.html
Smail,  I. (1998). The Hertzsprung-Russell Diagram of a Globular Cluster. Retrieved from http://community.dur.ac.uk/ian.smail/gcCm/gcCm_intro.html.