2021AJ....162....2K

The star RIK 90 is a member of a group of recently discovered young T Tauri stars showing complex periodic modulations of their light output, which have been difficult to explain. As one of the brightest, and having a relatively short period, RIK 90 is of particular interest. Thirty-three hours of contemporaneous BVR_CI_C photometry of the star are presented in this paper. An independent secondary periodicity was removed and the remainder of the data phased with the primary 0.25955 day period and smoothed to reveal the detailed structure of the light curves. The ratios of the amplitude in B to those in VR_CI_C are 1.2, 1.5, and 1.8. It is found that a collection of five cool starspots with temperatures in the range 2230-2550 K provides an excellent match to almost all observations, small-scale features in the I_C-band light curve being the notable exception. Starspot modeling of K2 observations of RIK 90 was also attempted. The morphology of the K2 light curve is entirely different from that discussed in this paper but could be accurately modeled by four dark starspots. In order to put these results into context, 15 other distinct K2 light curves belonging to 10 similarly variable T Tauri stars were also studied. Excellent fits were obtained to some of these with models consisting of large cool starspots. The majority of the remaining light curves could be modeled with a combination of hot and cold starspots.