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One of the central goals of the Spitzer Legacy Project ``From Molecular Coresto Planet-forming Disks'' (c2d) is to determine the frequency of remnantcircumstellar disks around weak-line T Tauri stars (wTTs) and to study theproperties and evolutionary status of these disks. Here we present a census ofdisks for a sample of over 230 spectroscopically identified wTTs located in thec2d IRAC (3.6, 4.5, 4.8, and 8.0 um) and MIPS (24 um) maps of the Ophiuchus,Lupus, and Perseus Molecular Clouds. We find that ~20% of the wTTs in amagnitude limited subsample have noticeable IR-excesses at IRAC wavelengthsindicating the presence of a circumstellar disk. The disk frequencies we findin these 3 regions are ~3-6 times larger than that recently found for a sampleof 83 relatively isolated wTTs located, for the most part, outside the highestextinction regions covered by the c2d IRAC and MIPS maps. The disk fractions wefind are more consistent with those obtained in recent Spitzer studies of wTTsin young clusters such as IC 348 and Tr 37. From their location in the H-Rdiagram, we find that, in our sample, the wTTs with excesses are among theyounger part of the age distribution. Still, up to ~50% of the apparentlyyoungest stars in the sample show no evidence of IR excess, suggesting that thecircumstellar disks of a sizable fraction of pre-main-sequence stars dissipatein a timescale of ~1 Myr. We also find that none of the stars in our sampleapparently older than ~10 Myrs have detectable circumstellar disks atwavelengths < 24 um. Also, we find that the wTTs disks in our sample exhibit awide range of properties (SED morphology, inner radius, L_DISK/L*, etc) whichbridge the gaps observed between the cTTs and the debris disk regimes.

The Spitzer c2d Survey of Weak-line T Tauri Stars II: New Constraints on the Timescale for Planet Building