Sub-second cadence structure of optical flares on AD Leo

¹ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly Thege út 15-17, H-1121 Budapest, Hungary
² HUN-REN RCAES, MTA Centre of Excellence, Budapest, Konkoly Thege út 15-17, H-1121 Budapest, Hungary
³ Eötvös University, Department of Astronomy, Pf. 32, 1518 Budapest, Hungary

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 21 November 2025
Accepted: 22 February 2026

Abstract

Context. Stellar flares are sudden brightenings caused by magnetic reconnection and are frequently observed on late-type stars. High-cadence photometry of flares provides valuable insights into the mechanisms of these events, yet such observations remain scarce.

Aims. We seek to explore the sub-second fine structure of stellar flares and assess the information content in high-speed photometry.

Methods. New 0.3 s-cadence photometry from a six-year-long observing campaign of the active M-dwarf AD Leo is presented. We use time–frequency analysis to detect quasi-periodic pulsations in the decay phase of flares. We explore statistical measures of time-series complexity of the detected flares to quantify the information gain achievable with high-cadence photometry.

Results. We detect 42 flares in 211 hours of observations. The flare frequency distribution is consistent with the previous literature. We find no quasi-periodic pulsations with periods below a few seconds, and identify two candidate signals with periods around 1 and 3 min. Using different measures of complexity on the binned flare light curves, we confirm the advantages of high observing cadence. However, we also find a plateau up to a binning of ≈4−5 s for a few complex flares, suggesting that an exposure time of a few seconds is usually enough to retain most of the information carried by a single-filter observation.

Conclusions. New photometric observations of AD Leo revealed sub-structures of flare light curves on a timescale of a few seconds, but we found no features on timescales below that.