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B-fields are predicted to play a role in the formation of filamentary structures and their fragmentation process. We aim at investigating the role of the B-field in the process of core fragmentation toward the hub-filament systems in the IRDC G14.2, which present different fragmentation level. We performed observations of the thermal dust polarization at 350 {\mu}m using the CSO toward the hubs. We applied the polarization--intensity-gradient method to estimate the significance of the B-field over the G-force. The B-field in Hub-N shows a uniform structure along the E-W orientation, perpendicular to the major axis of the hub-filament system. The I-gradient in Hub-N displays a local minimum coinciding with the dust core MM1a detected with interferometric observations. The B-field orientation is perturbed when approaching the dust core. Hub-S shows 2 local minima, reflecting the bimodal distribution of the B-field. In Hub-N, both E and W of the hub-filament system, the I-gradient and the B-field are parallel whereas they tend to be perpendicular when penetrating the filaments and hub. The analysis of the {\delta}- and {\Sigma} B-maps indicate that, the B-field cannot prevent the collapse, suggesting that the B-field is initially dragged by the infalling motion and aligned with it, or is channeling material toward the central ridge from both sides. Values of {\Sigma} B > 1 are found toward a N-S ridge encompassing the dust emission peak, indicating that in this region B-field dominates over G-force, or that with the current angular resolution we cannot resolve an hypothetical more complex structure. We estimated the B-field strength, the MtF ratio and the A-M number, and found differences between the 2 hubs. The different levels of fragmentation observed in these 2 hubs could arise from the differences in the B-field properties rather than from different intensity of the G-field., Comment: 14 pages, 9 figures

For the Class 0 protostar, L1527, we compare 131 polarization vectors from SCUPOL/JCMT, SHARP/CSO and TADPOL/CARMA observations with the corresponding model polarization vectors of four ideal-MHD, non-turbulent, cloud core collapse models. These four models differ by their initial magnetic fields before collapse; two initially have aligned fields (strong and weak) and two initially have orthogonal fields (strong and weak) with respect to the rotation axis of the L1527 core. Only the initial weak orthogonal field model produces the observed circumstellar disk within L1527. This is a characteristic of nearly all ideal-MHD, non-turbulent, core collapse models. In this paper we test whether this weak orthogonal model also has the best agreement between its magnetic field structure and that inferred from the polarimetry observations of L1527. We found that this is not the case; based on the polarimetry observations the most favored model of the four is the weak aligned model. However, this model does not produce a circumstellar disk, so our result implies that a non-turbulent, ideal-MHD global collapse model probably does not represent the core collapse that has occurred in L1527. Our study also illustrates the importance of using polarization vectors covering a large area of a cloud core to determine the initial magnetic field orientation before collapse; the inner core magnetic field structure can be highly altered by a collapse and so measurements from this region alone can give unreliable estimates of the initial field configuration before collapse., Comment: 43 pages, 9 figures, 4 tables. Accepted by the Astrophysical Journal

We report new 350 micron polarization observations of the thermal dust emission from the cores surrounding the low-mass, Class 0 YSOs L1527, IC348-SMM2 and B335. We have inferred magnetic field directions from these observations, and have used them together with results in the literature to determine whether magnetically regulated core-collapse and star-formation models are consistent with the observations. These models predict a pseudo-disk with its symmetry axis aligned with the core magnetic field. The models also predict a magnetic field pinch structure on a scale less than or comparable to the infall radii for these sources. In addition, if the core magnetic field aligns (or nearly aligns) the core rotation axis with the magnetic field before core collapse, then the models predict the alignment (or near alignment) of the overall pinch field structure with the bipolar outflows in these sources. We show that if one includes the distorting effects of bipolar outflows on magnetic fields, then in general the observational results for L1527 and IC348-SMM2 are consistent with these magnetically regulated models. We can say the same for B335 only if we assume the distorting effects of the bipolar outflow on the magnetic fields within the B335 core are much greater than for L1527 and IC348-SMM2. We show that the energy densities of the outflows in all three sources are large enough to distort the magnetic fields predicted by magnetically regulated models., Comment: Accepted for publication in The Astrophysical Journal

We report the discovery of a nearby, embedded cluster of young stellar objects, associated filamentary infrared dark cloud, and 4.5 micron shock emission knots from outflows detected in Spitzer/IRAC mid-infrared imaging of the Serpens-Aquila Rift obtained as part of the Spitzer Gould Belt Legacy Survey. We also present radial velocity measurements of the region from molecular line observations obtained with the Submillimeter Array (SMA) that suggest the cluster is co-moving with the Serpens Main embedded cluster 3 degrees to the north. We therefore assign it the same distance, 260 pc. The core of the new cluster, which we call Serpens South, is composed of an unusually large fraction of protostars (77%) at high mean surface density (>430 pc^-2) and short median nearest neighbor spacing (3700 AU). We perform basic cluster structure characterization using nearest neighbor surface density mapping of the YSOs and compare our findings to other known clusters with equivalent analyses available in the literature., Comment: 11 pages, 3 figures; Accepted to ApJ Letters; full resolution version at http://www.cfa.harvard.edu/~rgutermuth/preprints/gutermuth_serps.pdf

We present observations of 10.6 square degrees of the Perseus molecular cloud at 24, 70, and 160 microns with the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS). The image mosaics show prominent, complex extended emission dominated by illuminating B stars on the East side of the cloud, and by cold filaments of 160 micron emission on the West side. Of 3950 point sources identified at 24 microns, 1141 have 2MASS counterparts. A quarter of these populate regions of the Ks vs. Ks-[24] diagram that are distinct from stellar photospheres and background galaxies, and thus are likely to be cloud members with infrared excess. Nearly half (46%) of these 24 micron excess sources are distributed outside the IC 348 and NGC 1333 clusters. NGC 1333 shows the highest fraction of stars with flat or rising spectral energy distributions (28%), while Class II SEDs are most common in IC 348. These results are consistent with previous relative age determinations for the two clusters. The intercluster region contains several tightly clumped (r~0.1 pc) young stellar aggregates whose members exhibit a wide variety of infrared spectral energy distributions characteristic of different circumstellar environments. One possible explanation is a significant age spread among the aggregate members, such that some have had time to evolve more than others. Alternatively, if the aggregate members all formed at roughly the same time, then remarkably rapid circumstellar evolution would be required to account for the association of Class I and Class III sources at ages <~1 Myr. We highlight important results for several other objects as well (full abstract in the paper)., Comment: 82 pages, 32 figures, accepted to ApJS; ALL figures (even line drawings) had to be degraded to be accepted by the system here; the full-res figures are available in the version linked from the 'publications' area available at http://peggysue.as.utexas.edu/SIRTF/

We announce the discovery of SST-Lup3-1, a very low mass star close to the brown dwarf boundary in Lupus III with a circum(sub)stellar disk, discovered by the `Cores to Disks' Spitzer Legacy Program from mid-, near-infrared and optical data, with very conspicuous crystalline silicate features in its spectrum. It is the first of such objects with a full 5 to 35 micron spectrum taken with the IRS and it shows strong 10 and 20 micron silicate features with high feature to continuum ratios and clear crystalline features out to 33 micron. The dust in the disk upper layer has a crystalline silicate grain fraction between 15% and 33%, depending on the assumed dust continuum. The availability of the full Spitzer infrared spectrum allows an analysis of the dust composition as a function of temperature and position in the disk. The hot (~ 300 K) dust responsible for the 10 micron feature consists of a roughly equal mix of small (~ 0.1 micron) and large (~ 1.5 micron) grains, whereas the cold (~ 70 K) dust responsible for the longer wavelength silicate features contains primarily large grains (> 1 micron). Since the cold dust emission arises from deeper layers in the inner (< 3 AU) disk as well as from the surface layers of the outer (3-5 AU) disk, this provides direct evidence for combined grain growth and settling in the disk. The inferred crystalline mass fractions in the two components are comparable. Since only the inner 0.02 AU of the disk is warm enough to anneal the amorphous silicate grains, even the lowest fraction of 15% of crystalline material requires either very efficient mixing or other formation mechanisms., Comment: Accepted for publication in ApJ. 19 pages and 4 figures. V2 with correct references

We report the first detections of the Class 0 protostellar source IRAM 04191+1522 at wavelengths shortward of 60 microns with the Spitzer Space Telescope. We see extended emission in the Spitzer images that suggests the presence of an outflow cavity in the circumstellar envelope. We combine the Spitzer observations with existing data to form a complete dataset ranging from 3.6 to 1300 microns and use these data to construct radiative transfer models of the source. We conclude that the internal luminosity of IRAM 04191+1522, defined to be the sum of the luminosity from the internal sources (a star and a disk), is L_int = 0.08 +/- 0.04 L_sun, placing it among the lowest luminosity protostars known. Though it was discovered before the launch of the Spitzer Space Telescope, IRAM 04191+1522 falls within a new class of Very Low Luminosity Objects being discovered by Spitzer. Unlike the two other well-studied objects in this class, which are associated either with weak, compact outflows or no outflows at all, IRAM 04191+1522 has a well-defined molecular outflow with properties consistent with those expected based on relations derived from higher luminosity (L_int > 1 L_sun) protostars. We discuss the difficulties in understanding IRAM 04191+1522 in the context of the standard model of star formation, and suggest a possible explanation for the very low luminosity of this source., Comment: Accepted for publication in the Astrophysical Journal. 39 pages, 9 figures. See http://peggysue.as.utexas.edu/SIRTF/ for high-resolution figures

Using the Spitzer Space Telescope, we have observed 90 weak-line and classical T Tauri stars in the vicinity of the Ophiuchus, Lupus, Chamaeleon, and Taurus star-forming regions as part of the Cores to Disks (c2d) Spitzer Legacy project. In addition to the Spitzer data, we have obtained contemporaneous optical photometry to assist in constructing spectral energy distributions. These objects were specifically chosen as solar-type young stars with low levels of H alpha emission, strong X-ray emission, and lithium absorption i.e. weak-line T Tauri stars, most of which were undetected in the mid-to-far IR by the IRAS survey. Weak-line T Tauri stars are potentially extremely important objects in determining the timescale over which disk evolution 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. We find that only 5/83 weak-line T Tauri stars have detectable excess emission between 3.6 and 70 micron which would indicate the presence of dust from the inner few tenths of an AU out to the planet-forming regions a few tens of AU from the star. Of these sources, two have small excesses at 24 microns consistent with optically thin disks; the others have optically thick disks already detected by previous IR surveys. All of the seven classical T Tauri stars show excess emission at 24 and 70 micron, although their properties vary at the shorter wavelengths. Our initial results show that disks are rare among young stars selected for their weak H alpha emission., Comment: 29 pages, 9 figures, accepted for publication in ApJ

We present maps of over 1.5 square degrees in Chamaeleon (Cha) II at 24, 70, and 160 micron observed with the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) and a 1.2 square degree millimeter map from SIMBA on the Swedish-ESO Submillimetre Telescope (SEST). The c2d Spitzer Legacy Team's data reduction pipeline is described in detail. Over 1500 24 micron sources and 41 70 micron sources were detected by MIPS with fluxes greater than 10-sigma. More than 40 potential YSOs are identified with a MIPS and 2MASS color-color diagram and by their spectral indices, including two previously unknown sources with 24 micron excesses. Our new SIMBA millimeter map of Cha II shows that only a small fraction of the gas is in compact structures with high column densities. The extended emission seen by MIPS is compared with previous CO observations. Some selected interesting sources, including two detected at 1 mm, associated with Cha II are discussed in detail and their SEDs presented. The classification of these sources using MIPS data is found to be consistent with previous studies., Comment: 44 pages, 12 figures (1 color), to be published in ApJ

We present observations of L1014, a dense core in the Cygnus region previously thought to be starless, but data from the Spitzer Space Telescope shows the presence of an embedded source. We propose a model for this source that includes a cold core, heated by the interstellar radiation field, and a low-luminosity internal source. The low luminosity of the internal source suggests a substellar object. If L1014 is representative, other "starless" cores may turn out to harbor central sources., Comment: 7 pages, To appear in the ApJS Spitzer Special Edition