(Abridged) The c2d Spitzer Legacy project obtained images and photometry with both IRAC MIPS instruments for five large, nearby molecular clouds. This paper combines information drawn from studies of individual clouds into a combined updated statistical analysis star formation rates efficiencies, numbers lifetimes SED classes, clustering properties. Current efficiencies range 3% to 6%. Taken together, the are producing about 260 solar masses stars per Myr. surface density is more than an...

We present a uniform mid-infrared imaging and photometric survey of 36 young, nearby, star-forming clusters groups using {\it Spitzer} IRAC MIPS. have confidently identified classified 2548 young stellar objects recently established color-based methods. devised applied new algorithm for the isolation local surface density enhancements from point source distributions, enabling us to extract overdense cores observed star forming regions further analysis. compiled several basic structural...

view Abstract Citations (644) References (71) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense Cores in Dark Clouds. VIII. Velocity Gradients Goodman, A. ; Benson, P. J. Fuller, G. Myers, C. An analysis of motions consistent with uniform rotation dense cores is presented. Twenty-nine the 43 studied have a statistically significant gradient. Some gradients are spatially continuous and rotation, but other apparent caused by clump-clump motion, or sharp...

Crucial steps in the formation of stars and planets can be studied only at mid‐ to far‐infrared wavelengths, where Space Infrared Telescope (SIRTF) provides an unprecedented improvement sensitivity. We will use all three SIRTF instruments (Infrared Array Camera [IRAC], Multiband Imaging Photometer for [MIPS], Spectrograph [IRS]) observe sources that span evolutionary sequence from molecular cores protoplanetary disks, encompassing a wide range cloud masses, stellar star‐forming environments....

We present evidence for CO depletion toward the starless cloud core L1544. A comparison between C17O and 1.3 mm continuum dust emission shows that is depleted by a factor of ~10 at peak. Our observations are consistent with model in which condensed out onto grains densities above nd ~ 105 cm-3. The corresponding radius "depleted region" rd 6500 AU, we find this causes 2.3 M☉ gas to be lost view molecular line emission. Optically thin high-density tracers, such as HC18O+ D13CO+, show...

We present results of an extensive mapping survey N2H+(1-0) in about 60 low mass cloud cores already mapped the NH3(1,1) inversion transition line. The has been carried out at FCRAO antenna with angular resolution 1.5 times finer than previous ammonia observations. Cores stars typically have map sizes a factor two smaller for N2H+ NH3, indicating presence denser and more centrally concentrated gas compared to starless cores. Significant correlations are found between NH3 column densities...

The nearest young stellar groups are associated with "hubs" of column density exceeding 1022 cm−2, according to recent observations. These hubs radiate multiple "filaments" parsec length, having lower and fewer stars. Systems many filaments tend have parallel similar spacing. Such "hub–filament structure" is all the nine within 300 pc, forming low-mass Similar properties seen in infrared dark clouds more massive In a new model, an initial clump uniform medium compressed into...

We present near- and mid-infrared photometry obtained with the Spitzer Space Telescope of ∼300 known members IC 348 cluster. merge this existing ground-based optical near-infrared in order to construct optical-infrared spectral energy distributions (SEDs) for all cluster a complete atlas these SEDs. employ observations investigate both frequency nature circumstellar disk population The span wavelength range between 3.6 24 μm, corresponding radii ∼0.1-5 AU from central star. are sufficiently...

We have characterized the physical structure and chemical composition of two close-to-round starless cores in Taurus-Auriga, L1498 L1517B. Our analysis is based on high angular resolution observations at least transitions NH3, N2H+, CS, C34S, C18O, C17O, together with maps 1.2 mm continuum. For both cores, we derive radial profiles constant temperature turbulence, density distributions close to those non-singular isothermal spheres. Using these conditions a Monte Carlo radiative transfer...

We compare the infrared colors predicted by theoretical models of protostellar envelopes and protoplanetary disks with initial observations young stellar objects made Infrared Array Camera (IRAC) on Spitzer Space Telescope. Disk envelope characterized infall and/or accretion rates found in previous studies can quantitatively account for range IRAC four embedded clusters: S140, S171, NGC 7129, Cep C. The color-color diagram ([3.6]-[4.5] vs. [5.8]-[8.0]) be used to help distinguish between...

We present a comprehensive analysis of structure in the young, embedded cluster, NGC 1333 using members identified with Spitzer and 2MASS photometry based on their IR-excess emission. In total, 137 are this way, composed 39 protostars 98 more evolved pre-main sequence stars disks. Of latter class, four transition/debris disk candidates. The fraction exposed disks is 83% +/- 11%, showing that there measurable diskless population. sources each Class I II evolutionary states shown to have very...

We present a survey of the Orion A and B molecular clouds undertaken with IRAC MIPS instruments onboard Spitzer. In total, five distinct fields were mapped covering 9 sq. degrees in mid-IR bands spanning 3-24 microns. The includes Nebula Cluster, Lynds 1641, 1630 1622 dark clouds, NGC 2023, 2024, 2068 2071 nebulae. These data are merged 2MASS point source catalog to generate eight band photometry. identify 3479 dusty young stellar objects (YSOs) by searching for sources colors indicative...

We present evidence that low-mass starless cores, the simplest units of star formation, are systematically differentiated in their chemical composition. Some molecules, including CO and CS, almost vanish near core centers, where abundance decreases by at least 1 or 2 orders magnitude with respect to value outer core. At same time, N2H+ molecule has a constant abundance, fraction NH3 increases toward center. Our conclusions based on systematic study five mostly round cores (L1498, L1495,...

view Abstract Citations (530) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense cores in dark clouds. II. NH3 observations and star formation. Myers, P. C. ; Benson, J. All strong, 'dense core' sources (2, 2)-line are mapped the present results of a survey about 100 visually opaque regions nearby clouds 1.3-cm (J, K) = (1, 1) line NH3. Line shapes compared with cloud motion models, source density, size, temperature equilibrium stability...

We present an unbiased census of starless cores in Perseus, Serpens, and Ophiuchus, assembled by comparing large-scale Bolocam 1.1 mm continuum emission maps with Spitzer c2d surveys. use the catalogs to separate 108 from 92 protostellar core samples Enoch et al. (2006), Young (2007). A comparison these populations reveals initial conditions cores. Starless Perseus have similar masses but larger sizes lower densities on average than cores, that suggest density profiles substantially flatter...

We present a database of 264 cores mapped in the (J,K) = (1,1) and (2,2) lines NH3. list core gas properties—peak positions, total ammonia column densities, intrinsic line widths, kinetic temperatures, volume sizes, aspect ratios, velocity gradients, as well properties associated young stellar objects (YSOs)—associated IRAS sources along with their luminosities core-YSO distances, outflow velocities, SIMBAD cluster associations. also results our statistical analysis enumerate important...

The maps presented in Paper I are here used to infer the variation of column densities HCO+, DCO+, N2H+, and N2D+ as a function distance from dust peak. These results interpreted with aid crude chemical model that predicts abundances these species radius spherically symmetric radial density distribution inferred observations emission at millimeter wavelengths absorption infrared. Our main observational finding is N(N2D+)/N(N2H+) ratio order 0.2 toward L1544 peak compared N(DCO+)/N(HCO+) =...

We report observations of 47 candidate protostars in two optically thick lines [H2CO (212-111) and CS (2-1)] one thin line [N2H+ (1-0)] using the IRAM 30 m, SEST 15 Haystack 37 m radio telescopes. The sources were selected for redness their spectra (Tbol < 200 K) near distance (d 400 pc). Most have asymmetric, lines. observed distribution velocity differences, δV = (Vthick - Vthin)/ΔVthin, is skewed toward negative (blueshifted) velocities both H2CO samples. This excess much more significant...

view Abstract Citations (420) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense cores in dark clouds. III. Subsonic turbulence. Myers, P. C. Using published data, possible correlations among line widths and cloud size are examined for clouds which span the transition between supersonic subsonic motions. Plots show linear log width size, density presented discussed, as well a plot showing that most close to virial equilibrium. It is...

We have undertaken a survey of N2H+ and N2D+ toward 31 low-mass starless cores using the IRAM 30 m telescope. Our main objective has been to determine abundance ratio nuclei these thus obtain estimates degree deuterium enrichment, symptom advanced chemical evolution according current models. find that N(N2D+)/N(N2H+) is larger in more "centrally concentrated cores" with peak H2 column density than sample mean. The enrichment presently ascribed depletion CO high (>3 × 104 cm-3) core nucleus....

We present a multiline study of the dense core L1544 in Taurus molecular complex. Although does not harbor an embedded star, it presents several characteristics cores that have already undergone star formation, suggesting may be rather advanced its evolution toward becoming star-forming core. The spectral lines from interesting dichotomy, with thick gas tracers suffering very strong self absorption while CO and isotopes are being absorbed at all. presence absorptions allows us to both...

view Abstract Citations (428) References (89) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS X-Ray Sources in Regions of Star Formation. III. Naked T Tauri Stars Associated with the Taurus-Auriga Complex Walter, Frederick M. ; Brown, A. Mathieu, R. D. Myers, P. C. Vrba, F. J. The authors report results from a multispectral investigation stellar counterparts X-ray sources general region star-formation complex. They discuss 28 new low-mass pre-main-sequence...

This paper presents a large spectral line and continuum survey of 8 deeply embedded, low-mass protostellar cores using the Submillimeter Array. Each source was observed in high excitation lines some most common molecular species, CO, HCO+, CS, SO, H2CO, CH3OH SiO. Line emission from 11 species originating warm dense gas have been imaged at angular resolution (1-3"; typically 200-600 AU) together with 230 GHz (1.3 mm) 345 (0.8 mm). Compact is for all sources which likely originates marginally...

A simple analytic model of radiative transfer in two parts a contracting cloud matches wide range line profiles candidate infall regions and provides sensitive estimate Vin, the characteristic inward speed gas forming line. The assumes uniform equal temperature velocity dispersion σ, whose density are attenuation-weighted means over front rear halves centrally condensed, cloud. predicts two-peak for "slow" infall, Vin ≪ red-shoulder "fast" ~ σ. formula expresses solely terms σ observable...