Presentation #118.01 in the session “T Tauri Stars: Properties and Variability”.
High-precision time series photometry provides a unique window into the dynamics of the inner disk regions (< 1 AU) around young stars (< 5-10 Myr). Exquisite surveys carried out with CoRoT and Kepler/K2 have revealed a huge variety of photometric behaviors for young stars with disks, which range from purely periodic or quasi-periodic, to stochastic, bursting, or dipping. By exploring the color dependence of each variability pattern, it is possible to identify the underlying physical drivers: stellar magnetic activity, steady/unsteady star-disk interaction, variable mass accretion, rapidly evolving inner disk structures. In this contribution, we present a new study on the time domain behavior of very young stars in the Lagoon Nebula. The region, monitored during K2 Campaign 9, hosts a very young (~2 Myr) population distributed over a wide mass range, including dozens of OB stars. These characteristics render the region an ideal target to probe the impact of stellar mass and environmental conditions on the dynamics of young star-disk systems at the age when planets are born. From the K2 mosaic we extracted light curves for around 300 Lagoon Nebula members, of spectral types between B and K. For the same stars, we gathered auxiliary multi-band (u,g,r,i,Hα) photometry from the VLT Survey Telescope, to investigate the nature of the observed variability signatures. Our study reveals a clear distinction between weakly variable higher-mass stars and strongly variable lower-mass stars, with disk-related variability signatures that tend to disappear at spectral types earlier than G. Different light curve classes appear to be associated with different characteristic timescales of variability, suggesting a diverse physical origin of the corresponding variability signatures, which may arise from different locations in the star-inner disk environment. At the same time, all stars, irrespective of their light curve morphologies, are found to exhibit the largest amount of variability on timescales of days (which correspond to the typical rotation periods for these young objects), suggesting an overall stability of the inner disk structure over many dynamical timescales.