Understanding the flare emission in CF Tucanae using TESS

Abstract

Abstract Chromospherically active binaries are important in the understanding of the origins of optical flares. Since studies of flares in binaries are important, we perform a detailed analysis of 11 flares emitted by the RS CVn binary source CF Tucanae using the Transiting Exoplanet Survey Satellite (TESS). We assume a 10000 K blackbody spectrum to determine the flare energies, which were noted to be ∼0.29–2.86 × 1035 erg. We also fitted optical flares with a fast rise with an exponential decay burst profile and decay times were used to estimate the flare scale lengths. Three flares among them mandate a double burst model and another two exhibit complex flare features. Spot areas were found to be ∼1022 cm2 and associated magnetic energies were found to be ∼1036–37 erg. This excess of magnetic energy indicates that the flares release only a small fraction of the magnetic energy of the dominant spot but may indicate a lack of connection between the flares and the dominant spot. We also study the periodic variations using the times of minima obtained from TESS data along with previous values. The optical periodic variation requires a parabola and a sinusoidal function to get the best fit. A new periodic modulation of Pmod ∼ 28.64 ± 1.82 yr was observed and we attempt to explain this using a magnetic activity cycle. We conclude that CF Tuc exhibits complex flares and its periodic modulation varies, probably due to the exchange of spin and orbital angular momentum in the binary.