Most existing studies of young stellar populations have focused on the youngest (~ < 2-3 million year old) T Tauri stars, which are usually associated with their natal gas and hence easier to identify. In contrast, older T-Tauri stars (those with ages ~ 4 - 10 million years), being more difficult to find, have been less studied, even though they hold key insight to understanding evolution of lower-mass ( 0.1 - 2 M_sun ) stars and of protoplanetary discs. We present a study of photometric variability of 2000 confirmed 4-10 Myr T-Tauri stars in the Orion OB1 association using optical time-series from three different surveys: the Centro de Investigaciones de Astronomia-Quest Equatorial Survey Team (CIDA-QUEST), the Young Exoplanet Transit Initiative (YETI) and from a Kitt Peak National Observatory (KPNO) campaign. We investigated stellar properties such as rotation period and amplitude of variability based on star type and location to look for population-wide trends. We detected 563 periodic variables and 1437 non-periodic variables by investigating the light curves of these stars. We find that 29.59% of Weak-line T-Tauri stars (WTTS) and 19.45% of Classical T-Tauri stars (CTTS) are periodic. We did not find any noticeable difference in rotation period between CTTS and WTTS. In contrast, our study provides observational evidence of rotational evolution between 4 Myr and 10 Myr stars with the young ones having longer rotation periods. We also confirm the well known pattern of larger amplitude variability among CTTS when compared to WTTS, possibly originating in the interaction between the protoplanetary disc and the central star in the CTTS systems.
Publication:Karim et al., The rotation period distributions of 4--10 Myr T Tauri stars in Orion OB1: New constraints on pre-main-sequence angular momentum evolution, AJ, accepted in May 2016