UV variability and accretion dynamics in the young open cluster NGC 2264 | L. Venuti (Univ. Grenoble, Univ. Palermo) in Aula at 15:30 on 28 January 2015 (Wednesday)

Photometric variability is a defining property of T Tauri stars, manifest at a wide range of wavelengths and on different timescales (hours, days, months, years). Exploring YSOs variability across wavelength and time domain is of utmost importance in order to unveil the dynamics and mechanisms at play in different systems. In this talk, we present and discuss the mid-term variability of pre-main sequence stars in NGC 2264 (3 Myr) at UV and optical wavelengths. The bulk of the study is a 2 week-long u+r monitoring survey performed in February 2012 with CFHT/MegaCam, as a part of the CSI 2264 campaign (Cody et al. 2014). We find that accreting objects (CTTS) exhibit a significantly larger amount of variability than non-accreting members (WTTS), in the optical and especially in the UV. A definite correlation is observed between variability indicators and the measured UV excess for the former group; this suggests that accretion mechanisms have a primary impact on the observed variability amplitudes for CTTS. We investigate the (u-r) color variations that accompany magnitude variations for different classes of objects, and explore the connection between these color signatures and the physics of the systems. An extensive spot modeling of u-band and r-band variability amplitudes is performed to probe the nature of the variability displayed by NGC 2264 members. Finally, we compare the amount of mid-term variability with magnitude variations on shorter and longer timescales, in order to identify the leading timescales and contributions to u-band variability and assess its stability over the baselines investigated.