Modulation over 40 years: Independent and combined observations of RR Lyrae stars in M15

Using high-cadence observations of the globular cluster M15 obtained by the KAIT telescope at Mt. Hamilton, we present a determination of the periods, amplitudes, and types for 50+ variable stars in M15 as well as an independent catalog of detected variable stars. A separate 1-year observation of M15 obtained by the Nickel telescope at Mt. Hamilton covering the range of 6+ months is used to perform a long term analysis of period and amplitude modulation in these stars. We then combine our data with previously published datasets spanning more than 40 years to comment on the very long term trends seen in this population of RR Lyrae stars.