AC Andromedae is notable as a triple-mode radial pulsator, with three distinct periods at 0.711, 0.525, and 0.421 days. These periods interact with one another, producing an incredibly complex beat pattern in the light curve. No two nights of observation are ever the same, and you need very long spans of data to uncover its complex behavior. When the periods of a star are precisely determined, you can use them as tests of stellar pulsation models. In a 1994 study, Geza Kovacs and Robert Buchler tried to match these periods to models like RR Lyrae stars in both mass and composition, but couldn't. Instead, they matched them to more massive stars with higher metal abundances. For that reason, they suggest that AC Andromedae is more like the post-main sequence delta Scuti stars than the horizontal branch RR Lyrae stars.
This particular light curve is part of a multiseason time-series data set collected by Gerry Samolyk in 2008.