Browsing by Subject "RS CVn stars"

The class of RS Canum Venaticorum (RS CVn) variables are rapidly rotating, close detached Chromospherically Active Binary Stars (CABS). Their spectra show strong Ca II H and K emission lines, which indicate the presence of solar type chromospheric activity. Observed amplitudes of brightness variations in RS CVn stars are caused by large starspots. Their orbital periods are typically few days. EI Eridani (EI Eri) is an active, rapidly rotating (v sin i = 51 ± 0.5 km/s) binary star that belongs to the class of RS CVn variables. The primary component is a subgiant star with spectral type G5 IV. Its rotation and orbital motion are synchronised, i.e. P_rot = P_phot ≈ P_orb. We analyse 30 years of standard Johnson V differential photometry of EI Eri. The data were obtained with the Tennesee State University’s T3 0.4-meter Automatic Photometric Telescope (APT). We analyse the data with a new two-dimensional period finding method formulated by Jetsu (2019). This new method allows us to detect the real light curves of long-lived starspots of EI Eri. We also solve the parameters of these real light curves: periods, amplitudes and minimum epochs. Our analysis shows that the parameters of these real light curves are connected to long-lived starspots. There are also spatial correlations between these real light curve parameters. We detected two different period level starspot groups, P_1 ≈ 1.915920 ± 0.000079 days and P_2 ≈ 1.9472324 ± 0.0000040 days, rotating on the surface of EI Eri. The faster rotating starspots P_1 are non-stationary and the slower rotating starspots P_2 are stationary in the orbital reference of frame. The slower rotating starspots are at the longitudes coinciding with the line connecting the centres of the members of EI Eri. The slower rotating starspots have larger amplitudes than the faster rotating starspots. Hence, the slower rotating starspots are dominating the observed light curves. Our results show that the hypothesis, where the observed light curve is the sum of the real light curves (Jetsu, 2019), is valid for EI Eri. We can also show that the starspots of EI Eri are dark. The traditional one-dimensional period finding methods have given spurious results, like the rapid rotation period changes of starspots or abrupt longitudinal 180 degrees shifts of activity. Because of the short lap cycle period P_lap = 119.14 ± 0.30 days between the slower and the faster rotating starspots of EI Eri, the light curves have previously been misinterpreted.