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

## TL;DR

This paper introduces an adaptive elliptical aperture photometry software that enhances high-cadence ground-based photometry, enabling better detection of rapid stellar oscillations and improving light curve quality for variable star studies.

## Contribution

The paper presents a novel software package utilizing adaptive elliptical apertures for high-cadence photometry, demonstrating significant improvements over traditional methods and applying it to rapid oscillators observed from SAAO.

## Key findings

- Improved light curve quality for high-cadence observations.
- No high-frequency pulsations detected in the three studied Ap stars.
- Software is publicly available for community use.

## Abstract

Context. Modern space telescopes are currently providing high-precision light curves for a large fraction of the sky, such that many new variable stars are being discovered. However, some stars have periodic variability with periods of order minutes and require high-cadence photometry to probe the physical mechanisms responsible. A cadence of less than a minute is often required to remove Nyquist ambiguities and confirm rapid variability which forces observers to obtain high-cadence ground-based photometry. Aims. We aim to provide a modern software package to reduce ground-based photometric time series data and deliver optimised (differential) light curves. To produce high-quality light curves, which maximise the amplitude signal-to-noise ratio of short-period variability in a Fourier spectrum, we require adaptive elliptical aperture photometry as this represents a significant advantage compared to aperture photometry using circular apertures of fixed radii. Methods. The methodology of our code and its advantages are demonstrated using high-cadence ground-based photometry from the South African Astronomical Observatory (SAAO) of a confirmed rapidly oscillating Ap (roAp) star. Furthermore, we employ our software package to search for rapid oscillations in three candidate roAp stars. Results. We demonstrate that our pipeline represents a significant improvement in the quality of light curves, and we make it available to the community for use with different instruments and observatories. We search for and 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 HD 181810. Conclusions. We demonstrate the significant improvement in the extraction of short-period variability caused by high-frequency pulsation modes, and discuss the implication of null detections in three Ap stars.