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Context. Modern space telescopes are currently providing high-precision lightcurves for a large fraction of the sky, such that many new variable stars arebeing discovered. However, some stars have periodic variability with periods oforder minutes and require high-cadence photometry to probe the physicalmechanisms responsible. A cadence of less than a minute is often required toremove Nyquist ambiguities and confirm rapid variability which forces observersto obtain high-cadence ground-based photometry. Aims. We aim to provide amodern software package to reduce ground-based photometric time series data anddeliver optimised (differential) light curves. To produce high-quality lightcurves, which maximise the amplitude signal-to-noise ratio of short-periodvariability in a Fourier spectrum, we require adaptive elliptical aperturephotometry as this represents a significant advantage compared to aperturephotometry using circular apertures of fixed radii. Methods. The methodology ofour code and its advantages are demonstrated using high-cadence ground-basedphotometry from the South African Astronomical Observatory (SAAO) of aconfirmed rapidly oscillating Ap (roAp) star. Furthermore, we employ oursoftware package to search for rapid oscillations in three candidate roApstars. Results. We demonstrate that our pipeline represents a significantimprovement in the quality of light curves, and we make it available to thecommunity for use with different instruments and observatories. We search forand demonstrate the lack of high-frequency roAp pulsations to a limit of$\sim$1 mmag using B data in the three Ap stars HD 158596, HD 166542 and HD181810. Conclusions. We demonstrate the significant improvement in theextraction of short-period variability caused by high-frequency pulsationmodes, and discuss the implication of null detections in three Ap stars.

astronomy and astrophysics

Adaptive elliptical aperture photometry: a software package for  high-cadence ground-based photometry. I. Application to rapid oscillators  observed from SAAO