We report on the properties of pre-main-sequence objects in the Taurus molecular clouds as observed in 7 mid-and far-infrared bands with the Spitzer Space Telescope. There are 215 previously-identified members of the Taurus star-forming region in our ∼44 square degree map; these members exhibit a range of Spitzer colors that we take to define young stars still surrounded by circumstellar dust (noting that ∼20% of the bonafide Taurus members exhibit no detectable dust excesses). We looked for new objects in the survey field with similar Spitzer properties, aided -2by extensive optical, X-ray, and ultraviolet imaging, and found 148 candidate new members of Taurus. We have obtained follow-up spectroscopy for about half the candidate sample, thus far confirming 34 new members, 3 probable new members, and 10 possible new members, an increase of 15-20% in Taurus members. Of the objects for which we have spectroscopy, 7 are now confirmed extragalactic objects, and one is a background Be star. The remaining 93 candidate objects await additional analysis and/or data to be confirmed or rejected as Taurus members. Most of the new members are Class II M stars and are located along the same cloud filaments as the previously-identified Taurus members. Among non-members with Spitzer colors similar to young, dusty stars are evolved Be stars, planetary nebulae, carbon stars, galaxies, and AGN.Subject headings: stars: formation -stars: circumstellar matter -stars: pre-main sequenceinfrared: starswhere m is the reported magnitude (and F ν the flux density) for a given object, Z = 18.259, 17.204, and 14.837, and f = 1.94×10 −16 , 4.76×10 −16 , and 5.71×10 −15 ergs cm −2 s −1Å−1 counts −1 sec for U , UVW1, and UVW2 (respectively). In the equation, λ is in units ofÅ, and c is 3×10 18Å s −1 The effective wavelengths are 0.344, 0.291, and 0.212 µm for U , UVW1, and UVW2. There are ∼1600 objects with XMM-Newton OM flux densities in our catalog (0.2% of the entire catalog).We note that many of the X-ray detected XEST sources are likely background galaxies (see Güdel et al. 2007) and that XEST included regions not covered by our map, such as L1551.The XEST team assembled a catalog of supporting data from the literature, such as optical photometric measurements, for all of the previously-identified Taurus members (see §3.1.1 below); we have included these photometric points in our database, converting Johnson magnitudes to flux densities using zero-points available in the literature (e.g., Cox 2001 and references therein).The SEDs presented in this paper use all of these supporting data where available (except for the X-ray fluxes), and are presented as λF λ in cgs units (erg s −1 cm −2 ), against λ in microns.2 In SDSS, a "maggy" is the ratio of the flux density of the object to a standard flux density. The Sloan magnitudes are AB magnitudes, as opposed to Vega magnitudes. In the AB system, a flat spectrum object with 3631 Jy at each band should have every magnitude equal to zero, and all maggies equal to one. Flux densities returned by th...

We present initial results from time-series imaging at infrared wavelengths of 0.9 deg 2 in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5 μm data over 40 consecutive days. We extracted light curves with ∼3% photometric accuracy for ∼2000 ONC members ranging from several solar masses down to well below the hydrogen-burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (I c ) and/or near-infrared (JK s ) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 and 4.5 μm variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009 and highlight our light curves for AA-Tau analogs-YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs.

We present low-resolution (R=900) optical (576.1-1,051.1 nm) spectroscopic observations of 40 candidate very low-mass members in the Upper Scorpius OB association. These objects were selected using the I, J and K photometry available in the DENIS database. We have derived spectral types and we have measured Hα and NaI doublet (at 818.3 and 819.5 nm) equivalent widths. We assess the youth of the objects by comparing them to their older counterparts of similar spectral type in the Pleiades cluster and the field. Our analysis indicates that 28 of our targets are young very low-mass objects, and thus they are strong candidate members of the OB association. The other 12 DENIS sources are foreground M dwarfs or background red giants. Our sample of spectroscopic candidate members includes 18 objects with spectral types in the range M6.5 and M9, which are likely young brown dwarfs. We classify these candidates as accreting/non accreting using the scheme proposed by Barrado y Navascués & Martín (2003). We find 5 substellar-mass candidate cluster members that are still undergoing mass accretion, indicating that the timescale for accretion onto brown dwarfs can be as long as 5 Myr in some cases.

Context. Theoretical arguments suggest that dust grains should grow in the dense cold parts of molecular clouds. Evidence of larger grains has so far been gathered in near/mid infrared extinction and millimeter observations. Interpreting the data is, however, aggravated by the complex interplay of density and dust properties (as well as temperature for thermal emission). Aims. Direct evidence of larger particles can be derived from scattered mid-infrared (MIR) radiation from a molecular cloud observed in a spectral range where little or no emission from polycyclic aromatic hydrocarbons (PAHs) is expected. Methods. We present new Spitzer data of L183 in bands that are sensitive and insensitive to PAHs. The visual extinction A V map derived in a former paper was fitted by a series of 3D Gaussian distributions. For different dust models, we calculate the scattered MIR radiation images of structures that agree with the A V map and compare them to the Spitzer data. Results. The Spitzer data of L183 show emission in the 3.6 and 4.5 μm bands, while the 5.8 μm band shows slight absorption. The emission layer of stochastically heated particles should coincide with the layer of strongest scattering of optical interstellar radiation, which is seen as an outer surface on I band images different from the emission region seen in the Spitzer images. Moreover, PAH emission is expected to strongly increase from 4.5 to 5.8 μm, which is not seen. Hence, we interpret this emission to be MIR scattered light from grains located further inside the core, and call it "coreshine". Scattered light modeling when assuming interstellar medium dust grains without growth does not reproduce flux measurable by Spitzer. In contrast, models with grains growing with density yield images with a flux and pattern comparable to the Spitzer images in the bands 3.6, 4.5, and 8.0 μm. Conclusions. There is direct evidence of dust grain growth in the inner part of L183 from the scattered light MIR images seen by Spitzer.

We present observations of ∼7 square degrees of the North American and Pelican Nebulae region at 24, 70, and 160 µm with the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS). We incorporate the MIPS observations with earlier Spitzer Infrared Array Camera (IRAC) observations, as well as archival near-infrared (IR) and optical data. We use the MIPS data to identify 1286 young stellar object (YSO) candidates. IRAC data alone can identify 806 more YSO candidates, for a total of 2076 YSO candidates. Prior to the Spitzer observations, there were only ∼200 YSOs known in this region. Three subregions within the complex are highlighted as clusters: the Gulf of Mexico, the Pelican, and the Pelican's Hat. The Gulf of Mexico cluster is subject to the highest extinction (A V at least ∼30) and has the widest range of infrared colors of the three clusters, including the largest excesses and by far the most point-source detections at 70 µm. Just 3% of the cluster members were previously identified; we have redefined this cluster as about 10-100 times larger (in projected area) than was previously realized.

We present a 9 deg 2 map of the North American and Pelican Nebulae regions obtained in all four Infrared Array Camera (IRAC) channels with the Spitzer Space Telescope. The resulting photometry is merged with that at JHK s from Two Micron All Sky Survey and a more spatially limited BVI survey from previous ground-based work. We use a mixture of color-color diagrams to select a minimally contaminated set of more than 1600 objects that we claim are young stellar objects (YSOs) associated with the star-forming region. Because our selection technique uses infrared excess as a requirement, our sample is strongly biased against inclusion of Class III YSOs. The distribution of IRAC spectral slopes for our YSOs indicates that most of these objects are Class II, with a peak toward steeper spectral slopes but a substantial contribution from a tail of Flat spectrum and Class I type objects. By studying the small fraction of the sample that is optically visible, we infer a typical age of a few Myr for the low-mass population. The young stars are clustered, with about a third of them located in eight clusters that are located within or near the LDN 935 dark cloud. Half of the YSOs are located in regions with surface densities higher than 1000 YSOs/deg 2. The Class I objects are more clustered than the Class II stars.

Aims. We want to investigate whether brown dwarfs (BDs) form like stars or are ejected embryos. We study the presence of disks around BDs in the Taurus cloud, and discuss implications for substellar formation models. Methods. We use photometric measurements from the visible to the far infrared to determine the spectral energy distributions (SEDs) of Taurus BDs. Results. We use Spitzer color indices, Hα as an accretion indicator, and models fit to the SEDs in order to estimate physical parameters of the disks around these BDs. We study the spatial distribution of BDs with and without disks across the Taurus aggregates, and we find that BDs with and without disks are not distributed regularly across the Taurus cloud. Conclusions. We find that 48%±14% of Taurus BDs have a circumstellar disk signature, a ratio similar to recent results from previous authors in other regions. We fit the SEDs and find that none of the disks around BDs in Taurus can be fitted convincingly with a flaring index β = 0, indicating that heating by the central object is efficient and that the disks we observe retain a significant amount of gas. We find that BDs with disks are proportionally more numerous in the northern Taurus filament, possibly the youngest filament. We do not find such a clear segregation for classical T Tauri stars (CTTS) and weak-lined T Tauri stars (WTTS), suggesting that, in addition to the effects of evolution, any segregation effects could be related to the mass of the object. A by-product of our study is to propose a recalibration of the Barrado y Navascués & Martín (2003) accretion limit in the substellar domain. The global shape of the limit fits our data points if it is raised by a factor 1.25-1.30.

The Vulpecula OB association, Vul OB1, is a region of active star formation located in the Galactic plane at 2.3 kpc from the Sun. Previous studies suggest that sequential star formation is propagating along this 100 pc long molecular complex. In this paper, we use Spitzer MIPSGAL and GLIMPSE data to reconstruct the star formation history of Vul OB1, and search for signatures of past triggering events. We make a census of Young Stellar Objects (YSO) in Vul OB1 based on IR color and magnitude criteria, and we rely on the properties and nature of these YSOs to trace recent episodes of massive star formation. We find 856 YSO candidates, and show that the evolutionary stage of the YSO population in Vul OB1 is rather homogeneous -ruling out the scenario of propagating star formation. We estimate the current star formation efficiency to be ∼ 8%. We also report the discovery of a dozen pillar-like structures, which are confirmed to be sites of small scale triggered star formation.