Activity of the Young Star TOI 837 with an Exoplanet

Abstract—Based on high-precision data from the archive of the TESS space mission, a study was made of the photometric brightness variability of TOI 837—a young star with an exoplanet, a member of the southern sky cluster IC 2602. Based on all available observational results, we have estimated the star’s rotation period and brightness variability amplitude, and also estimated the absolute value of the spottedness parameter $A$ using the standard method. The area of spots on the surface of TOI 837 is from 21 600 up to 37 700 MSH and significantly exceeds the area of sunspots. The estimates were obtained for the effective temperature of the star ${{T}_{{{\text{eff}}}}} = 6047 \pm 162$ K and radius $R = 1.022{\kern 1pt} {{R}_{ \odot }}$. The manifestations of the TOI 837 flare activity in the observation interval in four sectors of the TESS space mission are studied and the two most reliable flares recorded are considered. The flare energies are $1.2 \times {{10}^{{35}}}$ erg and $2.1 \times {{10}^{{35}}}$ erg, and the probable value of the mass of the accompanying coronal mass ejection may reach ${{10}^{{21.4}}}$ g. We have estimated the most probable value of the TOI 837 activity cycle: it is 1500 days (4.1 years). A distinctive feature of TOI 837 b (as well as other exoplanets less than 100 million years old) is that its position on the diagrams “planet radius–age” and “planet radius–period of the planet’s rotation” does not overlap with populations of hot Jupiters and sub-Neptunes.