Benchmarking exoplanet transit depths with the SAAO Lesedi telescope

Abstract

The detection and characterisation of exoplanets through transit photometry is a cornerstone of modern astrophysics, enabling insights into planetary sizes, orbits, and host star properties. While space-based missions such as the Transiting Exoplanet Survey Satellite (TESS) and the Kepler Space Telescope have revolutionised the discovery of exoplanet candidates, ground-based telescopes remain crucial for validating these findings and refining their transit parameters with higher cadence and flexibility. This study evaluates the performance of the Lesedi telescope at the South African Astronomical Observatory (SAAO), equipped with the Mookodi instrument, for precise transit photometry of known exoplanets

By analysing transit light curves processed with AstroImageJ (AIJ), we assess Lesedi’s capability to detect and characterise transit signals under varying observational conditions. Our results show that Lesedi reliably detects transit depths between 10 and 20 parts per thousand (ppt), with image stacking techniques—particularly a five-frame rolling average—enabling sensitivity improvements down to approximately 1 ppt. These detection thresholds provide a practical framework for target selection, optimising observing strategies, and supporting complementary ground-based follow-up efforts worldwide.

Comparative analysis with the smaller NWU Nooitgedacht telescope highlights the critical influence of aperture size on photometric precision and demonstrates Lesedi’s enhanced suitability for shallow transit detection. This work thus establishes Lesedi and Mookodi as valuable tools in the global exoplanet validation network, bridging the gap between space-based discovery and detailed characterisation.

This research contributes to the improvement of observational methodologies for exoplanet studies, offering recommendations for exposure timing, target prioritisation, and data processing. It highlights the ongoing significance of ground-based facilities in advancing our understanding of exoplanetary systems, an era dominated by space missions.