Coherent brightness modulations in the dwarf nova AT Cancri

Abstract Light curves of the Z Cam type dwarf nova AT Cnc observed during standstill in 2016 and 2018 are analyzed. On the time scale of hours, previous reports on periodicities, in particular the presence of negative superhumps, could not be confirmed. Instead, a modulation with a period equal to the spectroscopic orbital period was detected which we thus interpret as a manifestations of the binary revolution. It enables us to derive a more accurate value of 0.201634  ±  0.000005 days (or its alias of 0.021580 days) for the period. AT Cnc also exhibits a hitherto unreported modulation of 25.731 ± 0.005 min, stable in period but not in amplitude over the entire time base of two years of the observations. We tentatively interpret this modulation in the context of an intermediate polar model for the system.