Browsing by Subject "stars: Formation"
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Item Alma Observations of the Massive Molecular Outflow G331.512-0.103(2013-09) Merello, Manuel; Bronfman, Leonardo; Garay, Guido; Lo, Nadia; Evans, Neal J., II; Nyman, Lars-Åke; Cortes, Juan R.; Cunningham, Maria R.; Merello, Merello; Evans, Neal J., IIThe object of this study is one of the most energetic and luminous molecular outflows known in the Galaxy, G331.512-0.103. Observations with ALMA Band 7 (350 GHz; 0.86 mm) reveal a very compact, extremely young bipolar outflow and a more symmetric outflowing shocked shell surrounding a very small region of ionized gas. The velocities of the bipolar outflow are about 70 km s(-1) on either side of the systemic velocity. The expansion velocity of the shocked shell is similar to 24 km s(-1), implying a crossing time of about 2000 yr. Along the symmetry axis of the outflow, there is a velocity feature, which could be a molecular "bullet" of high-velocity dense material. The source is one of the youngest examples of massive molecular outflow found associated with a high-mass star.Item The Bolocam Galactic Plane Survey. II. Catalog of the Image Data(2010-05) Rosolowsky, Erik; Dunham, Miranda K.; Ginsburg, Adam; Bradley, E. Todd; Aguirre, James; Bally, John; Battersby, Cara; Cyganowski, Claudia; Dowell, Darren; Drosback, Meredith; Evans, Neal J., II; Glenn, Jason; Harvey, Paul; Stringfellow, Guy S.; Walawender, Josh; Williams, Jonathan P.; Dunham, Miranda K.; Harvey, PaulWe present a catalog of 8358 sources extracted from images produced by the Bolocam Galactic Plane Survey (BGPS). The BGPS is a survey of the millimeter dust continuum emission from the northern Galactic plane. The catalog sources are extracted using a custom algorithm, Bolocat, which was designed specifically to identify and characterize objects in the large-area maps generated from the Bolocam instrument. The catalog products are designed to facilitate follow-up observations of these relatively unstudied objects. The catalog is 98% complete from 0.4 Jy to 60 Jy over all object sizes for which the survey is sensitive (<3'.5). We find that the sources extracted can best be described as molecular clumps-large dense regions in molecular clouds linked to cluster Formation. We find that the flux density distribution of sources follows a power law with dN/dS alpha S(-2.4+/-0.1) and that the mean Galactic latitude for sources is significantly below the midplane: < b > = (-0 degrees.095 +/- 0 degrees.001).Item The Bolocam Galactic Plane Survey. IX. Data Release 2 and Outer Galaxy Extension(2013-10) Ginsburg, Adam; Glenn, Jason; Rosolowsky, Erik; Ellsworth-Bowers, Timothy P.; Battersby, Cara; Dunham, Miranda; Merello, Manuel; Shirley, Yancy; Bally, John; Evans, Neal J., II; Stringfellow, Guy; Aguirre, James; Merello, Merello; Evans, Neal J., IIWe present a re-reduction and expansion of the Bolocam Galactic Plane Survey (BGPS), first presented by Aguirre et al. and Rosolowsky et al. The BGPS is a 1.1 mm survey of dust emission in the Northern galactic plane, covering longitudes -10 degrees < l < 90 degrees and latitudes vertical bar b vertical bar < 0 degrees.5with a typical 1 sigma rms sensitivity of 30-100 mJy in a similar to 33 '' beam. Version 2 of the survey includes an additional similar to 20 deg(2) of coverage in the third and fourth quadrants and similar to 2 deg(2) in the first quadrant. The new data release has improved angular recovery, with complete recovery out to similar to 80 '' and partial recovery to similar to 300", and reduced negative bowls around bright sources resulting from the atmospheric subtraction process. We resolve the factor of 1.5 flux calibration offset between the v1.0 data release and other data sets and determine that there is no offset between v2.0 and other data sets. The v2.0 pointing accuracy is tested against other surveys and is demonstrated to be accurate and an improvement over v1.0. We present simulations and tests of the pipeline and its properties, including measurements of the pipeline's angular transfer function. The Bolocat cataloging tool was used to extract a new catalog, which includes 8594 sources, with 591 in the expanded regions. We have demonstrated that the Bolocat 40 '' and 80 '' apertures are accurate even in the presence of strong extended background emission. The number of sources is lower than in v1.0, but the amount of flux and area included in identified sources is larger.Item The Bolocam Galactic Plane Survey. V. HCO+ and N2H+ Spectroscopy of 1.1 mm Dust Continuum Sources(2011-08) Schlingman, Wayne M.; Shirley, Yancy L.; Schenk, David E.; Rosolowsky, Erik; Bally, John; Battersby, Cara; Dunham, Miranda K.; Ellsworth-Bowers, Timothy P.; Evans, Neal J., II; Ginsburg, Adam; Stringfellow, Guy; Evans, Neal J., IIWe present the results of observations of 1882 sources in the Bolocam Galactic Plane Survey (BGPS) at 1.1 mm with the 10 m Henrich Hertz Telescope simultaneously in HCO+ J = 3-2 and N2H+ J = 3-2. We detect 77% of these sources in HCO+ and 51% in N2H+ at greater than 3 sigma. We find a strong correlation between the integrated intensity of both dense gas tracers and the 1.1 mm dust emission of BGPS sources. We determine kinematic distances for 529 sources (440 in the first quadrant breaking the distance ambiguity and 89 in the second quadrant). We derive the size, mass, and average density for this subset of clumps. The median size of BGPS clumps is 0.75 pc with a median mass of 330M(circle dot) (assuming T-Dust = 20 K). The median HCO+ linewidth is 2.9 km s(-1) indicating that BGPS clumps are dominated by supersonic turbulence or unresolved kinematic motions. We find no evidence for a size-linewidth relationship for BGPS clumps. We analyze the effects of the assumed dust temperature on the derived clump properties with a Monte Carlo simulation and find that changing the temperature distribution will change the median source properties (mass, volume-averaged number density, surface density) by factors of a few. The observed differential mass distribution has a power-law slope that is intermediate between that observed for diffuse CO clouds and the stellar initial mass function. BGPS clumps represent a wide range of objects (from dense cores to more diffuse clumps) and are typically characterized by larger sizes and lower densities than previously published surveys of high-mass star-forming regions. This collection of objects is a less-biased sample of star-forming regions in the Milky Way that likely span a wide range of evolutionary states.Item The Bolocam Galactic Plane Survey. XI. Temperatures and Substructure of Galactic Clumps Based on 350 ?M Observations(2015-05) Merello, Manuel; Evans, Neal J., II; Shirley, Yancy L.; Rosolowsky, Erik; Ginsburg, Adam; Bally, John; Battersby, Cara; Dunham, Miranda M.; Merello, Manuel; Evans, Neal J., IIWe present 107 maps of continuum emission at 350 mu m from Galactic molecular clumps. Observed sources were mainly selected from the Bolocam Galactic Plane Survey (BGPS) catalog, with three additional maps covering star-forming regions in the outer Galaxy. The higher resolution of the SHARC-II images (8."5 beam) compared with the 1.1 mm images from BGPS (33"beam) allowed us to identify a large population of smaller substructures within the clumps. A catalog is presented for the 1386 sources extracted from the 350 mu m maps. The color temperature distribution of clumps based on the two wavelengths has a median of 13.3 K and mean of 16.3 +/- 0.4 K, assuming an opacity law index of 1.7. For the structures with good determination of color temperatures, the mean ratio of gas temperature, determined from NH3 observations, to dust color temperature is 0.88 and the median ratio is 0.76. About half the clumps have more than 2 substructures and 22 clumps have more than 10. The fraction of the mass in dense substructures seen at 350 mu m compared to the mass of their parental clump is similar to 0.19, and the surface densities of these substructures are, on average, 2.2 times those seen in the clumps identified at 1.1 mm. For a well-characterized sample, 88 structures (31%) exceed a surface density of 0.2 g cm(-2), and 18 (6%) exceed 1.0 g cm(-2), thresholds for massive star Formation suggested by theorists.Item The Bolocam Galactic Plane Survey: Survey Description and Data Reduction(2011-01) Aguirre, James E.; Ginsburg, Adam G.; Dunham, Miranda K.; Drosback, Meredith M.; Bally, John; Battersby, Cara; Bradley, Eric Todd; Cyganowski, Claudia; Dowell, Darren; Evans, Neal J., II; Glenn, Jason; Harvey, Paul; Rosolowsky, Erik; Stringfellow, Guy S.; Walawender, Josh; Williams, Jonathan P.; Dunham, Miranda K.; Evans, Neal J., IIWe present the Bolocam Galactic Plane Survey (BGPS), a 1.1 mm continuum survey at 33 '' effective resolution of 170 deg(2) of the Galactic Plane visible from the northern hemisphere. The BGPS is one of the first large area, systematic surveys of the Galactic Plane in the millimeter continuum without pre-selected targets. The survey is contiguous over the range-10.5 <= l <= 90.5, vertical bar b vertical bar <= 0.5. Toward the Cygnus X spiral arm, the coverage was flared to vertical bar b vertical bar <= 1.5 for 75.5 <= l <= 87.5. In addition, cross-cuts to vertical bar b vertical bar <= 1.5 were made at l = 3, 15, 30, and 31. The total area of this section is 133 deg(2). With the exception of the increase in latitude, no pre-selection criteria were applied to the coverage in this region. In addition to the contiguous region, four targeted regions in the outer Galaxy were observed: IC1396 (9 deg(2), 97.5 <= l <= 100.5, 2.25 <= b <= 5.25), a region toward the Perseus Arm (4 deg(2) centered on l = 111, b = 0 near NGC 7538), W3/4/5 (18 deg(2), 132.5 <= l <= 138.5), and Gem OB1 (6 deg(2), 187.5 <= l <= 193.5). The survey has detected approximately 8400 clumps over the entire area to a limiting non-uniform 1s noise level in the range 11-53 mJy beam(-1) in the inner Galaxy. The BGPS source catalog is presented in a previously published companion paper. This paper details the survey observations and data reduction methods for the images. We discuss in detail the determination of astrometric and flux density calibration uncertainties and compare our results to the literature. Data processing algorithms that separate astronomical signals from time-variable atmospheric fluctuations in the data timestream are presented. These algorithms reproduce the structure of the astronomical sky over a limited range of angular scales and produce artifacts in the vicinity of bright sources. Based on simulations, we find that extended emission on scales larger than about 5'.9 is nearly completely attenuated (>90%) and the linear scale at which the attenuation reaches 50% is 3'.8. Comparison with other millimeter-wave data sets implies a possible systematic offset in flux calibration, for which no cause has been discovered. This presentation serves as a companion and guide to the public data release (http://irsa.ipac.caltech.edu/Missions/bolocam.html) through NASA's Infrared Processing and Analysis Center (IPAC) Infrared Science Archive (IRSA). New data releases will be provided through IPAC-IRSA with any future improvements in the reduction. The BGPS provides a complementary long-wavelength spectral band for the ongoing ATLASGAL and Herschel-SPIRE surveys, and an important database and context for imminent observations with SCUBA-2 and ALMA.Item A Candidate Detection of the First Hydrostatic Core(2010-10) Enoch, Melissa L.; Lee, Jeong-Eun; Harvey, Paul; Dunham, Michael M.; Schnee, Scott; Harvey, Paul; Dunham, Michael M.The first hydrostatic core (FHSC) represents a very early phase in the low-mass star Formation process, after collapse of the parent core has begun but before a true protostar has formed. This large (few AU), cool (100 K), pressure-supported core of molecular hydrogen is expected from theory, but has yet to be observationally verified. Here, we present observations of an excellent candidate for the FHSC phase: Per-Bolo 58, a dense core in Perseus that was previously believed to be starless. The 70 mu m flux of 65 mJy, from new deep Spitzer MIPS observations, is consistent with that expected for the FHSC. A low signal-to-noise detection at 24 mu m leaves open the possibility that Per-Bolo 58 could be a very low luminosity protostar, however. We utilize radiative transfer models to determine the best-fitting FHSC and protostar models to the spectral energy distribution and 2.9 mm visibilities of Per-Bolo 58. The source is consistent with an FHSC with some source of lower opacity through the envelope allowing 24 mu m emission to escape; a small outflow cavity and a cavity in the envelope are both possible. While we are unable to rule out the presence of a protostar, if present it would be one of the lowest luminosity protostellar objects yet observed, with an internal luminosity of similar to 0.01 L(circle dot).Item Dust, Ice, and Gas in Time (DIGIT) Herschel Observations of GSS30-IRS1 in Ophiuchus(2015-03) Je, Hyerin; Lee, Jeong-Eun; Lee, Seokho; Green, Joel D.; Evans, Neal J., II; ee, Jeong-Eun; Green, Joel D.; Evans, Neal J., IIAs a part of the "Dust, Ice, and Gas In Time" (DIGIT) key program on Herschel, we observed GSS30-IRS1, a Class I protostar located in Ophiuchus (d = 120 pc), with Herschel/Photodetector Array Camera and Spectrometer. More than 70 lines were detected within a wavelength range from 50 to 200 mu m, including CO, H2O, OH, and two atomic [O I] lines at 63 and 145 mu m. The [C II] line, known as a tracer of externally heated gas by the interstellar radiation field (ISRF), is also detected at 158 mu m. All lines, except [O I] and [C II], are detected only at the central spaxel of 9 ''.4 x 9 ''.4. The [O I] emissions are extended along a NE-SW orientation, and the [C II] line is detected over all spaxels, indicative of an external photodissociation region. The total [C II] intensity around GSS30 reveals that the far-ultraviolet radiation field is in the range of 3 to 20 G(0), where G(0) is in units of the Habing Field, 1.6 x 10(-3) erg cm(-2) s(-1). This enhanced external radiation field heats the envelope of GSS30-IRS1, causing the continuum emission to be extended, unlike the molecular emission. The best-fit continuum model of GSS30-IRS1 with the physical structure including flared disk, envelope, and outflow shows that the internal luminosity is 10 L-circle dot, and the region is externally heated by a radiation field enhanced by a factor of 130 compared to the standard local ISRF.Item Effect of Streaming Motion of Baryons Relative to Dark Matter on the Formation of the First Stars(2011-03) Stacy, Athena; Bromm, Volker; Loeb, Abraham; Stacy, Athena; Bromm, VolkerWe evaluate the effect of a supersonic relative velocity between the baryons and dark matter on the thermal and density evolution of the first gas clouds at z less than or similar to 50. Through a series of cosmological simulations, initialized at z(i) = 100 with a range of relative streaming velocities and minihalo Formation redshifts, we find that the typical streaming velocities will have little effect on the gas evolution. Once the collapse begins, the subsequent evolution of the gas will be nearly indistinguishable from the case of no streaming, and star Formation will still proceed in the same way, with no change in the characteristic Pop III stellar masses. Reionization is expected to be dominated by halo masses of greater than or similar to 10(8)M(circle dot), for which the effect of streaming should be negligible.Item First Science Results from SOFIA/FORCAST: Super-Resolution Imaging of the S140 Cluster at 37 Mu M(2012-04) Harvey, Paul M.; Adams, Joseph D.; Herter, Terry L.; Gull, George; Schoenwald, Justin; Keller, Luke D.; De Buizer, James M.; Vacca, William; Reach, William; Becklin, E. E.; Harvey, Paul M.We present 37 mu m imaging of the S140 complex of infrared sources centered on IRS1 made with the FORCAST camera on SOFIA. These observations are the longest wavelength imaging to resolve clearly the three main sources seen at shorter wavelengths, IRS 1, 2, and 3, and are nearly at the diffraction limit of the 2.5 m telescope. We also obtained a small number of images at 11 and 31 mu m that are useful for flux measurement. Our images cover the area of several strong submillimeter sources seen in the area-SMM 1, 2, and 3-that are not coincident with any mid-infrared sources and are not visible in our longer wavelength imaging either. Our new observations confirm previous estimates of the relative dust optical depth and source luminosity for the components in this likely cluster of early B stars. We also investigate the use of super-resolution to go beyond the basic diffraction limit in imaging on SOFIA and find that the van Cittert algorithm, together with the "multi-resolution" technique, provides excellent results.Item A Herschel Search for Cold Dust in Brown Dwarf Disks: First Results(2012-01) Harvey, Paul M.; Henning, Thomas; Menard, Francois; Wolf, Sebastian; Liu, Yao; Cieza, Lucas A.; Evans, Neal J., II; Pascucci, Ilaria; Merin, Bruno; Pinte, Christophe; Harvey, Paul M.; Evans, Neal J., IIWe report initial results from a Herschel program to search for far-infrared emission from cold dust around a statistically significant sample of young brown dwarfs. The first three objects in our survey are all detected at 70 mu m, and we report the first detection of a brown dwarf at 160 mu m. The flux densities are consistent with the presence of substantial amounts of cold dust in the outer disks around these objects. We modeled the spectral energy distributions (SEDs) with two different radiative transfer codes. We find that a broad range of model parameters provide a reasonable fit to the SEDs, but that the addition of our 70 mu m, and especially the 160 mu m, detection enables strong lower limits to be placed on the disk masses since most of the mass is in the outer disk. We find likely disk masses in the range of a few x 10(-6) to 10(-4) M(circle dot). Our models provide a good fit to the SEDs and do not require dust settling.Item Identifying the Low-Luminosity Population of Embedded Protostars in the c2d Observations of Clouds and Cores(2008-11) Dunham, Miranda M.; Crapsi, Antonio; Evans, Neal J., II; Bourke, Tyler L.; Huard, Tracy L.; Myers, Philip C.; Kauffmann, Jens; Dunham, Miranda M.; Crapsi, Antonio; Evans, Neal J., IIWe present the results of a search for all embedded protostars with internal luminosities <= 1.0 L(circle dot) in the full sample of nearby, low-mass star-forming regions surveyed by the Spitzer Space Telescope Legacy Project "From Molecular Cores to Planet Forming Disks'' (c2d). The internal luminosity of a source, L(int), is the luminosity of the central source and excludes luminosity arising from external heating. On average, the Spitzer c2d data are sensitive to embedded protostars with L(int) >= 4 x 10(-3)(d/140 pc)(2) L(circle dot), a factor of 25 better than the sensitivity of the Infrared Astronomical Satellite (IRAS) to such objects. We present a set of selection criteria used to identify candidates from the Spitzer data and examine complementary data to decide whether each candidate is truly an embedded protostar. We find a tight correlation between the 70 mu m flux and internal luminosity of a protostar, an empirical result based on both observations and detailed two-dimensional radiative transfer models of protostars. We identify 50 embedded protostars with L(int) <= 1: 0 L(circle dot); 15 have L(int) <= 0: 1 L(circle dot). The intrinsic distribution of source luminosities increases to lower luminosities. While we find sources down to the above sensitivity limit, indicating that the distribution may extend to luminosities lower than probed by these observations, we are able to rule out a continued rise in the distribution below L(int) = 0.1 L(circle dot). Between 75% and 85% of cores classified as starless prior to being observed by Spitzer remain starless to our luminosity sensitivity; the remaining 15%-25% harbor low-luminosity, embedded protostars. We compile complete spectral energy distributions for all 50 objects and calculate standard evolutionary signatures (L(bol), T(bol), and L(bol)/L(smm)) and argue that these objects are inconsistent with the simplest picture of star Formation, wherein mass accretes from the core onto the protostar at a constant rate.Item The Properties of Massive, Dense Clumps: Mapping Surveys of HCN and CS(2010-06) Wu, Jingwen; Evans, Neal J., II; Shirley, Yancy L.; Knez, Claudia; Evans, Neal J., IIWe have mapped over 50 massive, dense clumps with four dense gas tracers: HCN J = 1-0 and 3-2; and CS J = 2-1 and 7-6 transitions. Spectral lines of optically thin H(13)CN 3-2 and C(34)S 5-4 were also obtained toward the map centers. These maps usually demonstrate single well-peaked distributions at our resolution, even with higher J transitions. The size, virial mass, surface density, and mean volume density within a well-defined angular size ( FWHM) were calculated from the contour maps for each transition. We found that transitions with higher effective density usually trace the more compact, inner part of the clumps but have larger linewidths, leading to an inverse linewidth-size relation using different tracers. The mean surface densities are 0.29, 0.33, 0.78, 1.09 g cm(-2) within FWHM contours of CS 2-1, HCN 1-0, HCN 3-2, and CS 7-6, respectively. We find no correlation of L(IR) with surface density and a possible inverse correlation with mean volume density, contrary to some theoretical expectations. Molecular line luminosities L'(mol) were derived for each transition. We see no evidence in the data for the relation between L'(mol) and mean density posited by modelers. The correlation between L'(mol) and the virial mass is roughly linear for each dense gas tracer. No obvious correlation was found between the line luminosity ratio and infrared luminosity, bolometric temperature, or the L(IR)/M(Vir) ratio. A nearly linear correlation was found between the infrared luminosity and the line luminosity of all dense gas tracers for these massive, dense clumps, with a lower cutoff in luminosity at L(IR) = 10(4.5) L(circle dot). The L(IR)-L'(HCN1-0) correlation agrees well with the one found in galaxies. These correlations indicate a constant star Formation rate per unit mass from the scale of dense clumps to that of distant galaxies when the mass is measured for dense gas. These results support the suggestion that starburst galaxies may be understood as having a large fraction of gas in dense clumps.Item The Spitzer C2D Legacy Results: Star-Formation Rates and Efficiencies; Evolution and Lifetimes(2009-04) Evans, Neal J., II; Dunham, Michael M.; Jorgensen, Jes K.; Enoch, Melissa L.; Merin, Bruno; van Dishoeck, Ewine F.; Alcala, Juan M.; Myers, Philip C.; Stapelfeldt, Karl R.; Huard, Tracy L.; Allen, Lori E.; Harvey, Paul M.; van Kempen, Tim; Blake, Geoffrey A.; Koerner, David W.; Mundy, Lee G.; Padgett, Deborah L.; Sargent, Anneila I.; Evans, Neal J., II; Dunham, Michael M.; Harvey, Paul M.The c2d Spitzer Legacy project obtained images and photometry with both IRAC and MIPS instruments for five large, nearby molecular clouds. Three of the clouds were also mapped in dust continuum emission at 1.1 mm, and optical spectroscopy has been obtained for some clouds. This paper combines inFormation drawn from studies of individual clouds into a combined and updated statistical analysis of star-Formation rates and efficiencies, numbers and lifetimes for spectral energy distribution (SED) classes, and clustering properties. Current star-Formation efficiencies range from 3% to 6%; if star Formation continues at current rates for 10 Myr, efficiencies could reach 15-30%. Star-Formation rates and rates per unit area vary from cloud to cloud; taken together, the five clouds are producing about 260 M(circle dot) of stars per Myr. The star-Formation surface density is more than an order of magnitude larger than would be predicted from the Kennicutt relation used in extragalactic studies, reflecting the fact that those relations apply to larger scales, where more diffuse matter is included in the gas surface density. Measured against the dense gas probed by the maps of dust continuum emission, the efficiencies are much higher, with stellar masses similar to masses of dense gas, and the current stock of dense cores would be exhausted in 1.8 Myr on average. Nonetheless, star Formation is still slow compared to that expected in a free-fall time, even in the dense cores. The derived lifetime for the Class I phase is 0.54 Myr, considerably longer than some estimates. Similarly, the lifetime for the Class 0 SED class, 0.16 Myr, with the notable exception of the Ophiuchus cloud, is longer than early estimates. If photometry is corrected for estimated extinction before calculating class indicators, the lifetimes drop to 0.44 Myr for Class I and to 0.10 for Class 0. These lifetimes assume a continuous flow through the Class II phase and should be considered median lifetimes or half-lives. Star Formation is highly concentrated to regions of high extinction, and the youngest objects are very strongly associated with dense cores. The great majority (90%) of young stars lie within loose clusters with at least 35 members and a stellar density of 1 M(circle dot) pc(-3). Accretion at the sound speed from an isothermal sphere over the lifetime derived for the Class I phase could build a star of about 0.25 M(circle dot), given an efficiency of 0.3. Building larger mass stars by using higher mass accretion rates could be problematic, as our data confirm and aggravate the "luminosity problem" for protostars. At a given T(bol), the values for L(bol) are mostly less than predicted by standard infall models and scatter over several orders of magnitude. These results strongly suggest that accretion is time variable, with prolonged periods of very low accretion. Based on a very simple model and this sample of sources, half the mass of a star would be accreted during only 7% of the Class I lifetime, as represented by the eight most luminous objects.Item The Spitzer C2D Survey of Large, Nearby, Interstellar Clouds. XI. Lupus Observed With IRAC and MIPS(2008-08) Merin, Bruno; Jorgensen, Jes; Spezzi, Loredana; Alcala, Juan M.; Evans, Neal J., II; Harvey, Paul M.; Prusti, Timo; Chapman, Nicholas; Huard, Tracy; van Dishoeck, Ewine F.; Comeron, Fernando; Evans, Neal J., II; Harvey, Paul M.We present c2d Spitzer IRAC observations of the Lupus I, III, and IV dark clouds and discuss them in combination with optical, near-infrared, and c2d MIPS data. With the Spitzer data, the new sample contains 159 stars, 4 times larger than the previous one. It is dominated by low- and very low mass stars, and it is complete down to M approximate to 0.1 M-circle dot. We find 30%-40% binaries with separations between 100 and 2000 AU with no apparent effect on the disk properties of the members. A large majority of the objects are Class II or III objects, with only 20 (12%) Class I or flat-spectrum sources. The disk sample is complete down to "debris" -like systems in stars as small as M approximate to 0.2 M-circle dot and includes substellar objects with larger IR excesses. The disk fraction in Lupus is 70%-80%, consistent with an age of 1-2 Myr. However, the young population contains 20% optically thick accretion disks and 40% relatively less flared disks. A growing variety of inner disk structures is found for larger inner disk clearings for equal disk masses. Lupus III is themost centrally populated and rich, followed by Lupus I with a filamentary structure and by Lupus IV, where a very high density core with little star Formation activity has been found. We estimate star Formation rates in Lupus of 2-10 M-circle dot Myr(-1) and star Formation efficiencies of a few percent, apparently correlated with the associated cloud masses.Item The Spitzer C2D Survey of Nearby Dense Cores: Jet and Molecular Outflow Associated With A Young Stellar Object in Core A of L1251(2010-01) Lee, Jeong-Eun; Lee, Ho-Gyu; Shinn, Jong-Ho; Dunham, Miranda M.; Kim, Il-Suk; Kim, Chang-Hee; Bourke, Tyler L.; Evans, Neal J., II; Choi, Yunhee; Dunham, Miranda M.; Evans, Neal J., IIA long infrared jet has been discovered by the Spitzer c2d Legacy Program in core A of L1251. It is associated with a very embedded Class 0 object with an accretion luminosity of about 0.9 L(circle dot) derived by radiative transfer model fitting to the observed spectral energy distribution. Comparing the observed Infrared Array Camera colors along the infrared jet with those calculated from a model of an admixture of gas with a power-law temperature distribution indicates that the jet is possibly created by a paraboloidal bow shock propagating into the ambient medium of n(H(2)) = 10(5) cm(-3). In addition, the variation of the power-law index along the jet suggests that the portion of hot gas decreases with distance from the jet engine. The molecular outflow in this region has been mapped for the first time using CO data. From the calculated outflow momentum flux, a very strong lower limit to the average accretion luminosity is 3.6 sin i/cos(3) i L(circle dot), indicative of a decrease in the accretion rate with time.Item The Spitzer Infrared Spectrograph Survey of T Tauri Stars in Taurus(2011-07) Furlan, E.; Luhman, K. L.; Espaillat, C.; D'Alessio, P.; Adame, L.; Manoj, P.; Kim, K. H.; Watson, D. M.; Forrest, W. J.; McClure, M. K.; Calvet, N.; Sargent, B. A.; Green, Joel D.; Fischer, W. J.; Green, Joel D.We present 161 Spitzer Infrared Spectrograph (IRS) spectra of T Tauri stars and young brown dwarfs in the Taurus star-forming region. All of the targets were selected based on their infrared excess and are therefore surrounded by protoplanetary disks; they form the complete sample of all available IRS spectra of T Tauri stars with infrared excesses in Taurus. We also present the IRS spectra of seven Class 0/I objects in Taurus to complete the sample of available IRS spectra of protostars in Taurus. We use spectral indices that are not significantly affected by extinction to distinguish between envelope-and disk-dominated objects. Together with data from the literature, we construct spectral energy distributions for all objects in our sample. With spectral indices derived from the IRS spectra we infer disk properties such as dust settling and the presence of inner disk holes and gaps. We find a transitional disk frequency, which is based on objects with unusually large 13-31 mu m spectral indices indicative of a wall surrounding an inner disk hole, of about 3%, and a frequency of about 20% for objects with unusually large 10 mu m features, which could indicate disk gaps. The shape and strength of the 10 mu m silicate emission feature suggests weaker 10 mu m emission and more processed dust for very low mass objects and brown dwarfs (spectral types M6-M9). These objects also display weaker infrared excess emission from their disks, but do not appear to have more settled disks than their higher-mass counterparts. We find no difference for the spectral indices and properties of the dust between single and multiple systems.Item The Spitzer Survey of Interstellar Clouds in the Gould Belt. II. the Cepheus Flare Observed With IRAC and MIPS(2009-11) Kirk, Jason M.; Ward-Thompson, Derek; Di Francesco, James; Bourke, Tyler L.; Evans, Neal J., II; Merin, Bruno; Allen, Lori E.; Cieza, Lucas A.; Dunham, Michael M.; Harvey, Paul; Huard, Tracy; Jorgensen, Jes K.; Miller, Jennifer F.; Noriega-Crespo, Alberto; Peterson, Dawn; Ray, Tom P.; Rebull, Luisa M.; Dunham, Michael M.; Harvey, PaulWe present Spitzer Infrared Array Camera (IRAC; similar to 2 deg(2)) and Multiband Imaging Photometer for Spitzer (MIPS; similar to 8 deg(2)) observations of the Cepheus Flare, which is associated with the Gould Belt, at an approximate distance of similar to 300 pc. Around 6500 sources are detected in all four IRAC bands, of which similar to 900 have MIPS 24 mu m detections. We identify 133 young stellar object (YSO) candidates using color-magnitude diagram techniques, and a large number of the YSO candidates are associated with the NGC 7023 reflection nebula. Cross-identifications were made with the Guide Star Catalog II and the IRAS Faint Source Catalog, and spectral energy distributions (SEDs) were constructed. SED modeling was conducted to estimate the degree of infrared excess. It was found that a large majority of disks were optically thick accreting disks, suggesting that there has been little disk evolution in these sources. Nearest neighbor clustering analysis identified four small protostellar groups (L1228, L1228N, L1251A, and L1251B) with 5-15 members each and the larger NGC 7023 association with 32 YSO members. The star-Formation efficiency for cores with clusters of protostars and for those without clusters was found to be similar to 8% and similar to 1%, respectively. The cores L1155, L1241, and L1247 are confirmed to be starless down to our luminosity limit of L(bol) = 0.06 L(circle dot).Item The Spitzer Survey of Interstellar Clouds in the Gould Belt. III. A Multi-Wavelength View of Corona Australis(2011-06) Peterson, Dawn E.; Garatti, Alessio Caratti O.; Bourke, Tyler L.; Forbrich, Jan; Gutermuth, Robert A.; Jorgensen, Jes K.; Allen, Lori E.; Patten, Brian M.; Dunham, Michael M.; Harvey, Paul M.; Merin, Bruno; Chapman, Nicholas L.; Cieza, Lucas A.; Huard, Tracy L.; Knez, Claudia; Prager, Brian; Evans, Neal J., II; Dunham, Michael M.; Harvey, Paul M.; Evans, Neal J., IIWe present Spitzer Space Telescope IRAC and MIPS observations of a 0.85 deg(2) field including the Corona Australis (CrA) star-forming region. At a distance of 130 pc, CrA is one of the closest regions known to be actively forming stars, particularly within its embedded association, the Coronet. Using the Spitzer data, we identify 51 young stellar objects (YS0s) in CrA which include sources in the well-studied Coronet cluster as well as sources distributed throughout the molecular cloud. Twelve of the YSOs discussed are new candidates, one of which is located in the Coronet. Known YSOs retrieved from the literature are also added to the list, and a total of 116 candidate YSOs in CrA are compiled. Based on these YSO candidates, the star Formation rate is computed to be 12M(circle dot) Myr(-1), similar to that of the Lupus clouds. A clustering analysis was also performed, finding that the main cluster core, consisting of 68 members, is elongated (having an aspect ratio of 2.36), with a circular radius of 0.59 pc and mean surface density of 150 pc(-2). In addition, we analyze outflows and jets in CrA by means of new CO and H-2 data. We present 1 3 mm interferometric continuum observations made with the Submillimeter Array (SMA) covering R CrA, IRS 5, IRS 7, and IRAS 18595-3712 (IRAS 32). We also present multi-epoch H2 maps and detect jets and outflows, study their proper motions, and identify exciting sources. The Spitzer and ISAAC/VET observations of IRAS 32 show a bipolar precessing jet, which drives a CO(2-1) outflow detected in the SMA observations. There is also clear evidence for a parsec-scale precessing outflow, which is east west oriented and originates in the SMA 2 region and likely driven by SMA 2 or IRS 7A.Item The Taurus Spitzer Survey: New Candidate Taurus Members Selected Using Sensitive Mid-Infrared Photometry(2010-02) Rebull, L. M.; Padgett, D. L.; McCabe, C. E.; Hillenbrand, L. A.; Stapelfeldt, K. R.; Noriega-Crespo, A.; Carey, S. J.; Brooke, T.; Huard, T.; Terebey, S.; Audard, M.; Monin, J. L.; Fukagawa, M.; Gudel, M.; Knapp, G. R.; Menard, Francois; Allen, L. E.; Angione, J. R.; Baldovin-Saavedra, C.; Bouvier, J.; Briggs, K.; Dougados, C.; Evans, Neal J., II; Flagey, N.; Guieu, S.; Grosso, N.; Glauser, A. M.; Harvey, Paul; Hines, D.; Latter, W. B.; Skinner, S. L.; Strom, S.; Tromp, J.; Wolf, Sebastian; Evans, Neal J., II; Harvey, PaulWe report on the properties of pre-main-sequence objects in the Taurus molecular clouds as observed in seven mid-and far-infrared bands with the Spitzer Space Telescope. There are 215 previously identified members of the Taurus star-forming region in our similar to 44 deg(2) map; these members exhibit a range of Spitzer colors that we take to define young stars still surrounded by circumstellar dust (noting that similar to 20% of the bona fide Taurus members exhibit no detectable dust excesses). We looked for new objects in the survey field with similar Spitzer properties, aided by extensive optical, X-ray, and ultraviolet imaging, and found 148 new candidate members of Taurus. We have obtained follow-up spectroscopy for about half the candidate sample, thus far confirming 34 new members, three probable new members, and 10 possible new members, an increase of 15%-20% in Taurus members. Of the objects for which we have spectroscopy, seven 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 active galactic nuclei.