Correlated optical and X-ray variability in Classical T Tauri Stars | E. Flaccomio ( INAF- Osservatorio Astronomico di Palermo )

Young stars in the Classical T Tauri phase are characterized by complex and highly dynamical phenomena involving the stars, their circumstellar disks, mass accretion, and outflows. Quite unsurprisingly, high energy processes, as traced by, e.g., the X-ray emission, are affected or even driven by the interaction between these components. Because of the widely different characteristic temperatures of the involved physical components and of the dynamical nature of their interactions, coordinated multi-wavelength time-variability studies are best suited to their investigation. In March 2008, we have observed NGC 2264 with CoRoT for 23.5 days obtaining high-quality uninterrupted optical light-curves of its young stars. During the CoRoT pointing, two short Chandra observations were performed with a separation of 16 days, allowing us to study the correlation between optical and X-ray variability on this timescale, and thus the physical mechanism responsible for the variability. The variabilities of Classical T Taury Stars (CTTS) in the optical and soft X-ray (0.5-1.5 keV) bands are correlated, while no correlation is apparent in the hard (1.5-8.0 keV) band. Also, no correlation in either band is present for Weak line T Tauri stars. The correlation between soft X-ray and optical variability of CTTSs can be naturally explained in terms of time-variable shading (absorption) from circumstellar material orbiting the star, in a scenario rather similar to the one invoked to explain the observed phenomenology in the CTTS AA Tau. The slope of the observed correlation implies (in the hypothesis of homogeneous shading) a significant dust depletion in the circumstellar material.