Spitzer Cores to Disks Legacy Team Photometry of Weak-Line T Tauri Stars
          Deborah Padgett, Spitzer Science Center
          Karl Stapelfeldt, JPL
          David Koerner, Northern Arizona University
          Anneila Sargent, Caltech
          Neal Evans, U. Texas
          Lucas Cienza, U. Texas
          The c2d Team (UT, UMaryland, Caltech, Leiden, NAU, JPL)

          The Cores to disks (c2d) Spitzer Legacy project is observing ~170 weak-line T Tauri stars in and around the Ophiuchus, Lupus, Chamaeleon, and Taurus star- forming regions. These objects were specifically chosen as 1-10 Myr stars without IRAS or ISO detections of IR excess. Weak-line T Tauri stars are potentially extremely important objects in determining the timescale over which planet formation may take place. Our objective is to determine whether these young stars are diskless or have remnant disks which are below the detection threshold of previous infrared missions. Our Spitzer IRAC and MIPS observations provide 3.6 - 70 micron spectral energy distributions at unprecedented sensitivity. Preliminary MIPS results for the first 40 targets show that the great majority of weak-line T Tauri stars lack detectable 24 and 70 micron excess emission, which would indicate the presence of dust in the terrestrial planet-forming regions a few AU from the star. This result suggests that a significant fraction of young, solar-type stars are ''born diskless'' (i.e., are without disk excess prior to dispersing from their natal clouds). Another possibility is that current lists of weak-line T Tauri stars are heavily contaminated by foreground stars of Pleiades age. We will present an update of this program as of March 2005