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We present a census of the population of deeply embedded young stellar objects (YSOs) in the Ophiuchus molecular cloud complex based on a combination of Spitzer Space Telescope mid-infrared data from the "Cores to Disks" (c2d) legacy team and JCMT/SCUBA submillimeter maps from the COMPLETE team. We have applied a method developed for identifying embedded protostars in Perseus to these data sets and in this way construct a relatively unbiased sample of 27 candidate embedded protostars with envelopes more massive than our sensitivity limit (about 0.1 M). As in Perseus, the mid-infrared sources are located close to the center of the SCUBA cores and the narrowness of the spatial distribution of mid-infrared sources around the peaks of the SCUBA cores suggests that no significant dispersion of the newly formed YSOs has occurred. Embedded YSOs are found in 35% of the SCUBA cores--fewer than in Perseus (58%). On the other hand the mid-infrared sources in Ophiuchus have less red mid-infrared colors, possibly indicating that they are less embedded. We apply a nearest neighbor surface density algorithm to define the substructure in each of the clouds and calculate characteristic numbers for each subregion--including masses, star formation efficiencies, fraction of embedded sources, etc. Generally the main clusters in Ophiuchus and Perseus (L1688, NGC 1333, and IC 348) are found to have higher star formation efficiencies than small groups such as B1, L1455, and L1448, which on the other hand are completely dominated by deeply embedded protostars. We discuss possible explanations for the differences between the regions in Perseus and Ophiuchus, such as different evolutionary timescales for the YSOs or differences, e.g., in the accretion in the two clouds.

We present observations of two areas totalling 0.57 deg2 in the IC 5146 star-forming region at 3.6, 4.5, 5.8, 8.0, 24, and 70 mm observed with the Spitzer Space Telescope. We reexamine the issue of the distance to this cloud and conclude a value of 950 +- 80 pc is most likely. We compare source counts, colors, and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. We identify more than 200 young stellar object (YSO) candidates from color-magnitude and color-color diagrams, many of which were previously unknown. We compare the colors of these YSOs to the models of Robitaille et al. and perform simple fits to the SED's to estimate properties of the circumstellar disks likely to surround the Class II and III sources. We also compare the mid-IR disk excesses to Ha emission-line data where available. We present a quantitative description of the degree of clustering, estimate the star formation efficiency, and discuss the fraction of YSOs in the region with disks relative to an estimate of the diskless YSO population. Finally, we compare the YSO distribution to the cold dust distribution mapped by SCUBA and briefly describe the diffuse emission likely due to PAHs associated with the H II region.

We discuss the results from the combined IRAC and MIPS c2d Spitzer Legacy survey observations and complementary optical and NIR data of the Chamaeleon II (Cha II) dark cloud. We perform a census of the young population in an area of ~1.75 deg2 and study the spatial distribution and properties of the cloud members and candidate pre-main-sequence (PMS) objects and their circumstellar matter. Our census is complete down to the substellar regime ( M [?] 0.03 M). From the analysis of the volume density of the PMS objects and candidates we find two groups of objects with volume densities higher than 25 M pc [?]3 and 5-10 members each. A multiplicity fraction of about 13% +- 3% is observed for objects with separations 0.8'' < th < 6.0'' (142-1065 AU). No evidence for variability between the two epochs of the c2d IRAC data set, D t [?] 6 hr, is detected. We estimate a star formation efficiency of 1%-4%, consistent with the estimates for Taurus and Lupus, but lower than for Cha I. This might mean that different star formation activities in the Chamaeleon clouds reflect a different history of star formation. We also find that Cha II is turning some 6-7 M into stars every Myr, which is low in comparison with the star formation rate in other c2d clouds. The disk fraction of 70%-80% that we estimate in Cha II is much higher than in other star-forming regions and indicates that the population in this cloud is dominated by objects with active accretion. Finally, the Cha II outflows are discussed; a new Herbig-Haro outflow, HH 939, driven by the classical T Tauri star Sz 50, has been discovered.

We present maps of 14.4 deg2 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 and 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 mm and 81 sources at 70 mm at the 10 s 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 mm detections in the SWIRE extragalactic survey. We find that more than half of the YSO candidates, and almost all those with protostellar Class I spectral energy distributions, are confined to the known cluster and aggregates.

We present IRAC (3.6, 4.5, 5.8, and 8.0 mm) observations of the Chamaeleon II molecular cloud. The observed area covers about 1 deg2 defined by AV > 2. Analysis of the data in the 2005 c2d catalogs reveals a small number of sources (40) with properties similar to those of young stellar or substellar objects (YSOs). The surface density of these YSO candidates is low, and contamination by background galaxies appears to be substantial, especially for sources classified as Class I or flat spectral energy distribution (SED). We discuss this problem in some detail and conclude that very few of the candidate YSOs in early evolutionary stages are actually in the Cha II cloud. Using a refined set of criteria, we define a smaller, but more reliable, set of 24 YSO candidates.

We present maps of 0.89 deg2 of the Serpens dark cloud at 3.6, 4.5, 5.8, and 8.0 mm observed with the Spitzer Space Telescope Infrared Array Camera (IRAC). We discuss in detail the data processing carried out by the c2d team on IRAC data. More than 100,000 compact sources have been extracted, but we confine most of our discussion to the most reliable subset of these sources. This includes those that are detected above 7 s in all four IRAC bands or those detected in the two shorter IRAC bands together with 2MASS. We estimate completeness limits for our survey from Monte Carlo tests with artificial sources inserted into the Spitzer maps. We compare source counts, colors, and magnitudes in the Serpens cloud to two reference data sets, a 0.10 deg2 set of low-extinction regions near the dark cloud and a 1 deg2 subset of the SWIRE Elais N1 data that was processed through our pipeline. We find that it is possible to identify more than 200 young stellar object (YSO) candidates from color-magnitude and color-color diagrams, most of which were previously unknown. In addition to the dense area of new star formation known before in the "core" region (cluster A), we also find a moderately rich area to the south (cluster B). Our mapped area also includes the Herbig Ae star VV Ser, whose Spitzer images have been carefully modeled in a separate study. The extreme sensitivity of Spitzer IRAC allows us to search to very low luminosity limits for young substellar objects. The comparison of the Serpens region with the reference areas suggests that a population of infrared excess sources exists in Serpens at least down to luminosities of L ~ 10-3 L and possibly lower.

Infrared ~5-35 mm spectra for 40 solar mass T Tauri stars and 7 intermediate-mass Herbig Ae stars with circumstellar disks were obtained using the Spitzer Space Telescope as part of the c2d IRS survey. This work complements prior spectroscopic studies of silicate infrared emission from disks, which were focused on intermediate-mass stars, with observations of solar mass stars limited primarily to the 10 mm region. The observed 10 and 20 mm silicate feature strengths/shapes are consistent with source-to-source variations in grain size. A large fraction of the features are weak and flat, consistent with micron-sized grains indicating fast grain growth (from 0.1 to 1.0 mm in radius). In addition, approximately half of the T Tauri star spectra show crystalline silicate features near 28 and 33 mm, indicating significant processing when compared to interstellar grains. A few sources show large 10-to-20 mm ratios and require even larger grains emitting at 20 mm than at 10 mm. This size difference may arise from the difference in the depth into the disk probed by the two silicate emission bands in disks where dust settling has occurred. The 10 mm feature strength versus shape trend is not correlated with age or Ha equivalent width, suggesting that some amount of turbulent mixing and regeneration of small grains is occurring. The strength versus shape trend is related to spectral type, however, with M stars showing significantly flatter 10 mm features (larger grain sizes) than A/B stars. The connection between spectral type and grain size is interpreted in terms of the variation in the silicate emission radius as a function of stellar luminosity, but could also be indicative of other spectral-type-dependent factors (e.g., X-rays, UV radiation, and stellar/disk winds).