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Mid-Infrared Variation in Young Stars

Since 2003, the Spitzer Space Telescope has provided groundbreaking views of Galactic star formation in bands from 3.6 past 24 microns. During the cryogenic mission (the first 5.5 years), variability of young stars at these bands was noted, although typically with just a few epochs of observation. The cryogen ran out in 2009, and we are now in the warm mission era where the shortest two bands (3.6 and 4.5 microns) continue to function essentially as before. The phenomenal sensitivity and stability of Spitzer at these bands has enabled several dedicated monitoring programs studying the variability of young stars at timescales from minutes to years. The largest of these programs is YSOVAR (Stauffer et al.), but there are several smaller programs as well. With at least as many as 2200 young star light curves likely to come out of this, these programs as a whole enable more detailed study of the young star-disk interaction in the infrared for a wider range of ages and masses than has ever been accomplished before. Early results suggest a wide variety of sources of variability, including dust clouds in the disk, disk warps, star spots, and accretion. This contribution will review some of the most recent results from these programs.