Identification and characterization of 15 265 super-Nyquist frequencies in 1309 δ Scuti stars from Kepler photometry

The frequency of the pressure (p) mode in δScuti stars can exceed the Nyquist limit of Keple long-cadence photometry. These “superNyquist frequencies” (SNFs) are observed as “reflected” peaks at lower frequencies, i.e., they are Nyquist aliases that pose a threat to asteroseismic diagnostics. Their impact on δ Scuti p modes has yet to be comprehensively explored. We performed a systematic survey to search for SNFs in 1838 Kepler δ
Scuti stars through a novel technique based on a sliding Lomb-Scargle periodogram, identifying 15 265 confirmed SNFs in 1309 stars, from a total of 259 883 frequencies. We observe that the total number of detected frequencies per star remains featureless across the δ Scuti instability strip; however, young stars pulsate in higher frequencies and so have significantly more SNFs on average. Both the number and the rate of SNFs diminish accordingly as δ Scuti stars become more evolved, which is consistent with both observation and stellar models. Furthermore, our method detects a greater fraction of modes as SNFs at higher frequencies, rising from approximately 1% at 20 μHz to 23% at the Nyquist limit. The rate of underdetection is highest amongst low-amplitude modes. The SNF modulation patterns can be well distinguished from phase modulations induced by binarity or nonlinear mode interactions. We provide a frequency catalog for future asteroseismic studies of δ Scuti stars, wherein we identify each peak as being real or an alias, enabling further investigations into regular patterns of pulsation modes, linear combination frequencies, and theoretical modeling.