Unveiling the spectacular over 24-hour flare of star CD-36 3202

¹ Astronomical Institute, University of Wrocław, Kopernika 11, 51-622 Wrocław, Poland
e-mail: bicz@astro.uni.wroc.pl
² University of Wrocław, Centre of Scientific Excellence – Solar and Stellar Activity, Kopernika 11, 51-622 Wrocław, Poland

Received: 7 September 2023
Accepted: 24 November 2023

Abstract

We studied the light curve of the star CD-36 3202, which was observed by TESS for the presence of stellar spots and to analyze the rotationally modulated flare that took place on TESS Barycentric Julian Date 1486.93. Our main aims are to model the light curve of this flare and to estimate its location regarding stellar spots. The flare lasted approximately 27 h. Using our new tool, findinc_mc, we managed to estimate the inclination angle of the star to 70° ± 8°. With BASSMAN, we modeled the light curve of the CD-36 3202 and estimated that three spots are present on its surface. The mean temperature of the spots was about 4000 ± 765 K, and their total area amounted to 11.61% ± 0.13% on average. We created a new tool, named MFUEA, to model rotationally modulated flares, and used it to estimate the latitude of the long-duration flare event, finding 69₋₁⁺² deg. Our estimation of the flare location is the first recreation of the exact position of a flare in relation to starspots. The flare is placed 12° from the center of the coolest spot. This means that the flare is related to the magnetic processes above the active region represented by the spot. Removing the effects of rotational modulation from the flare light curve allowed us to correct the estimation of bolometric energy released during the event from (1.15 ± 0.35) × 10³⁵ erg to (3.99 ± 1.22) × 10³⁵ erg.