2025A&A...699A.322X

Aims. Understanding flare activity in RS CVn stars is crucial for elucidating their magnetic activity properties. This study aims to conduct a detailed statistical analysis of stellar flare characteristics in RS CVn-type stars using data from the Transiting Exoplanet Survey Satellite (TESS) and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) surveys.
Methods. We initially identified 80 305 candidates from the International Variable Star Index (VSX) and refined the sample to 1812 RS CVn stars through SIMBAD cross-matching. Using TESS two-minute cadence data, we processed 958 light curves from 246 targets, detecting 1254 flare events among 144 flare stars. By cross-matching with the LAMOST Data Release 10 (DR10) data, we obtain 148 and 482 low-resolution and medium-resolution spectra for 90 and 37 RS CVn-type sources, respectively. With LAMOST data, we calculated and statistically analysed several stellar magnetic activity indicators, such as Hα equivalent width. Combining Gaia survey, TESS Input Catalog, and LAMOST survey data, we investigated relationships between flare parameters and stellar characteristics.
Results. Of the 1,254 observed flare events, more than 89% had durations < 1 h, and more than 90% had amplitudes < 0.01. The flare stars concentrate within temperature (4000-6500 K), mass (< 1 M_⊙), and radius (0-5 R_⊙) ranges, with 21 stars deriving parameters from their primary components. The flare occurrence percentage is higher for temperatures in the range 3000-4000 K and orbital periods < 10 days. The duration (τ) is related to the energy (E) by the power law τ ∝ E^0.3–0.41. The power-law index, α, of the cumulative flare frequency distribution is about 1.22 ± 0.09. We analysed flare rotational phases and find no preference, indicating random occurrence. Medium-resolution spectra reveal asymmetry in the Hα profiles of one source, TIC 46296256, which might be caused by coronal rain, binary motion, or chromospheric condensation.