While searches for young stellar objects (YSOs) with the Spitzer Space Telescope focused on known molecular clouds, photometry from the Wide-field Infrared Survey Explorer (WISE) can be used to extend the search to the entire sky. As a precursor to more expansive searches, we present results for a 100 square degree region centered on the Canis Major clouds.
We present maps of 14.4 deg^2 of the Ophiuchus dark clouds observed by the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS). These high quality maps depict both numerous point sources as well as extended dust emission within the star-forming and non-star-forming portions of these clouds. Using PSF-fitting photometry, we detect 5779 sources at 24 um and 81 sources at 70 um at the 10 sigma level of significance. Three hundred twenty-three candidate young stellar objects (YSOs) were identified according to their positions on the MIPS/2MASS K versus K$-$[24] color-magnitude diagrams as compared to 24 um detections in the SWIRE extragalactic survey. We find that more than half of the YSO candidates, and almost all the ones with protostellar Class I spectral energy distributions, are confined to the known cluster and aggregates.
One of the central goals of the Spitzer Legacy Project ``From Molecular Cores to Planet-forming Disks (c2d) is to determine the frequency of remnant circumstellar disks around weak-line T Tauri stars (wTTs) and to study the properties and evolutionary status of these disks. Here we present a census of disks for a sample of over 230 spectroscopically identified wTTs located in the c2d 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 a magnitude limited subsample have noticeable IR-excesses at IRAC wavelengths indicating the presence of a circumstellar disk. The disk frequencies we find in these 3 regions are ~3-6 times larger than that recently found for a sample of 83 relatively isolated wTTs located, for the most part, outside the highest extinction regions covered by the c2d IRAC and MIPS maps. The disk fractions we find are more consistent with those obtained in recent Spitzer studies of wTTs in young clusters such as IC 348 and Tr 37. From their location in the H-R diagram, we find that, in our sample, the wTTs with excesses are among the younger part of the age distribution. Still, up to ~50% of the apparently youngest stars in the sample show no evidence of IR excess, suggesting that the circumstellar disks of a sizable fraction of pre-main-sequence stars dissipate in a timescale of ~1 Myr. We also find that none of the stars in our sample apparently older than ~10 Myrs have detectable circumstellar disks at wavelengths < 24 um. Also, we find that the wTTs disks in our sample exhibit a wide range of properties (SED morphology, inner radius, L_DISK/L*, etc) which bridge the gaps observed between the cTTs and the debris disk regimes.
