A<i>SPITZER</i>IRS STUDY OF INFRARED VARIABILITY IN TRANSITIONAL AND PRE-TRANSITIONAL DISKS AROUND T TAURI STARS

Abstract

We present a Spitzer IRS study of variability in 14 T Tauri stars in the\nTaurus and Chamaeleon star-forming regions. The sample is composed of\ntransitional and pre-transitional objects which contain holes and gaps in their\ndisks. We detect variability between 5-38 microns in all but two of our objects\non timescales of 2-3 years. Most of the variability observed can be classified\nas seesaw behavior, whereby the emission at shorter wavelengths varies\ninversely with the emission at longer wavelengths. For many of the objects we\ncan reasonably reproduce the observed variability using irradiated disk models,\nparticularly by changing the height of the inner disk wall by ~20%. When the\ninner wall is taller, the emission at the shorter wavelengths is higher since\nthe inner wall dominates the emission at 2-8 microns. The taller inner wall\ncasts a larger shadow on the outer disk wall, leading to less emission at\nwavelengths beyond 20 microns where the outer wall dominates. We discuss how\nthe possible presence of planets in these disks could lead to warps which cause\nchanges in the height of the inner wall. We also find that crystalline\nsilicates are common in the outer disks of our objects and that in the four\ndisks in the sample with the most crystalline silicates, variability on\ntimescales of 1 week is present. In addition to explaining the infrared\nvariability described above, planets can create shocks and collisions which can\ncrystallize the dust and lead to short timescale variability.\n