Characterizing UV variability and accretion in the young open cluster NGC 2264 | Laura Venuti (Institut de Planetologie et d’Astrophysique de Grenoble )

Characterizing UV variability and accretion in the young open cluster NGC 2264
I will present the results of an extensive UV/optical variability survey of the young open cluster NGC 2264 (3 Myr), performed at CFHT/MegaCam as a part of a wide project of simultaneous multi-wavelength (X-rays to IR) monitoring aimed at unambiguously characterizing YSO variability (the Coordinated Synoptic Investigation of NGC 2264). A complete u,g,r,i photometric dataset has been obtained for more than 700 young stars, ranging in mass from 0.2 to 2 MSun, and their u-band and r-band variability monitored over two full weeks. The u-band observations offer a direct access to the accretion features, hence providing a unique clue to the accretion dynamics throughout the region. I investigate the photometric properties of different stellar groups on various color-color and color-magnitude diagrams and infer a straightforward characterization based on accretion properties. I analyze the u-band variability of T Tauri stars on week timescales and probe the color signatures of different physical processes, showing that well-distinguished behaviors are specific to processes of different nature. Based on the UV excess diagnostics, I derive a dynamical picture of accretion in NGC 2264. I investigate the dependence of the inferred mass accretion rates on stellar mass and discuss the large spread in values detected at each mass. I explore the variability of the mass accretion rates on a timescale of weeks, resulting from the geometric effects linked with stellar rotation and from the intrinsic accretion variability, and show that this variability cannot explain the observed spread.