Accretion dynamics and disk evolution in NGC 2264: a study based on CoRoT photometric observations

Context. The young cluster NGC 2264 was observed with the CoRoT satellite for 23 days uninterruptedly in March 2008 with unprecedented photometric accuracy. We present the first results of our analysis of the accreting population belonging to the cluster as observed by CoRoT. Aims. We search for possible light curve variability of the same nature as that observed in the classical T Tauri star AA Tau, which was attributed to a magnetically controlled inner disk warp. The inner warp dynamics is supposed to be directly associated with the interaction between the stellar magnetic field and the inner disk region. Methods. We analyzed the CoRoT light curves of 83 previously known classical T Tauri stars that belong to NGC 2264 classifying them according to their light-curve morphology. We also studied the CoRoT light-curve morphology as a function of a Spitzer-based classification of the star-disk systems. Results. The classification derived on the basis of the CoRoT light-curve morphology agrees very well with the Spitzer IRAC-based classification of the systems. The percentage of AA Tau-like light curves decreases as the inner disk dissipates, from 40% +/- 10% in systems with thick inner disks to 36% +/- 16% in systems with anemic disks and zero in naked photosphere systems. Indeed, 91% +/- 29% of the CTTS with naked photospheres exhibit pure spot-like variability, while only 18% +/- 7% of the thick disk systems do so, presumably those seen at low inclination and thus free of variable obscuration. Conclusions. AA Tau-like light curves are found to be fairly common, with a frequency of at least similar to 30 to 40% in young stars with inner dusty disks. The temporal evolution of the light curves indicates that the structure of the inner disk warp, located close to the corotation radius and responsible for the obscuration episodes, varies over a timescale of a few (similar to 1-3) rotational periods. This probably reflects the highly dynamical nature of the star-disk magnetospheric interaction.