Spitzer Space Telescope - General Observer Proposal #60109 Measuring YSO inner accretion disk sizes, structure and dynamics with staring mode observations of 14 YSOs in Rho Ophiuchus Principal Investigator: Peter Plavchan Institution: California Institute of Technology Technical Contact: Peter Plavchan, California Institute of Technology Co-Investigators: John Stauffer, IPAC/SSC Rachel Akeson, IPAC/NExScI Sean Carey, IPAC/SSC John Carpenter, Caltech David Ciardi, IPAC/NExScI Kevin Covey, CfA Robert Gutermuth, CfA Patrick Ogle, IPAC/SSC Luisa Rebull, IPAC/SSC Karl Stapelfeldt, JPL Barbara Whitney, Space Science Science Category: young stellar objects Observing Modes: IRAC Post-Cryo Mapping Hours Approved: 24.0 Abstract: Variability is almost a defining characteristic of young stellar objects (YSOs). We propose a program to monitor YSOs with IRAC channel 2 in staring mode for 3 sets of 8 hours. This proposal is complementary to our Exploration Science Spitzer program YSOVAR, which measures variability on timescales greater than 4 hours. With the proposed observations, we will probe disk accretion dynamics on timescales from ~1 minute to 4 hours. Furthermore, we will carry out a novel application of the AGN reverberation mapping technique to YSOs to measure inner disk edge sizes. Combined with ground-based contemporaneous near-IR monitoring, we will be able to measure light travel time delays as short as 25 seconds from the reprocessed dust emission (~0.05 AU). We have constructed a model that confirms the feasibility of measuring these short time-lags, and it requires high-precision mid-infrared photometry that only Spitzer can provide. We have selected a field of 8 nearby, bright Class I and II YSOs in Rho Ophiuchus that contains known near-infrared variables to carry out this pilot program.