Browsing by Subject "dust, extinction"
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Item The Afterglows Of Swift-Era Gamma-Ray Bursts. I. Comparing Pre-Swift And Swift-Era Long/Soft (Type II) Grb Optical Afterglows(2010-09) Kann, D. A.; Klose, S.; Zhang, B.; Malesani, D.; Nakar, E.; Pozanenko, A.; Wilson, A. C.; Butler, N. R.; Jakobsson, Pall; Schulze, S.; Andreev, M.; Antonelli, L. A.; Bikmaev, I. F.; Biryukov, V.; Bottcher, M.; Burenin, R. A.; Ceron, J. M. C.; Castro-Tirado, A. J.; Chincarini, G.; Cobb, B. E.; Covino, S.; D'Avanzo, P.; D'Elia, V.; Della Valle, M.; Postigo, A. D.; Efimov, Y.; Ferrero, P.; Fugazza, D.; Fynbo, Johan P. U.; Galfalk, M.; Grundahl, F.; Gorosabel, J.; Gupta, S.; Guziy, S.; Hafizov, B.; Hjorth, J.; Holhjem, K.; Ibrahimov, M.; Im, M.; Israel, G. L.; Jelinek, M.; Jensen, B. L.; Karimov, R.; Khamitov, I. M.; Kiziloglu, U.; Klunko, E.; Kubanek, P.; Kutyrev, A. S.; Laursen, P.; Levan, A. J.; Mannucci, F.; Martin, C. M.; Mescheryakov, A.; Mirabal, N.; Norris, J. P.; Ovaldsen, J. E.; Paraficz, D.; Pavlenko, E.; Piranomonte, S.; Rossi, A.; Rumyantsev, V.; Salinas, R.; Sergeev, A.; Sharapov, D.; Sollerman, Jesper; Stecklum, B.; Stella, L.; Tagliaferri, G.; Tanvir, N. R.; Telting, J.; Testa, V.; Updike, A. C.; Volnova, A.; Watson, D.; Wiersema, K.; Xu, D.; Wilson, A. C.We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.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. III. Characterizing Physical Properties Of Massive Star-Forming Regions In The Gemini Ob1 Molecular Cloud(2010-07) Dunham, Miranda K.; Rosolowsky, Erik; Evans, Neal J.; Cyganowski, Claudia J.; Aguirre, James; Bally, John; Battersby, Cara; Bradley, Eric Todd; Dowell, Darren; Drosback, Meredith; Ginsburg, Adam; Glenn, Jason; Harvey, Paul; Merello, Manuel; Schlingman, Wayne; Shirley, Yancy L.; Stringfellow, Guy S.; Walawender, Josh; Williams, Jonathan P.; Dunham, Miranda K.; Evans, Neal J.; Harvey, Paul; Merello, ManueWe present the 1.1 mm Bolocam Galactic Plane Survey (BGPS) observations of the Gemini OB1 molecular cloud complex, and targeted NH3 observations of the BGPS sources. When paired with molecular spectroscopy of a dense gas tracer, millimeter observations yield physical properties such as masses, radii, mean densities, kinetic temperatures, and line widths. We detect 34 distinct BGPS sources above 5 sigma = 0.37 Jy beam(-1) with corresponding 5s detections in the NH3(1,1) transition. Eight of the objects show water maser emission (20%). We find a mean millimeter source FWHM of 1.12 pc and a mean gas kinetic temperature of 20 K for the sample of 34 BGPS sources with detections in the NH3(1,1) line. The observed NH3 line widths are dominated by non-thermal motions, typically found to be a few times the thermal sound speed expected for the derived kinetic temperature. We calculate the mass for each source from the millimeter flux assuming the sources are isothermal and find a mean isothermal mass within a 120 '' aperture of 230 +/- 180 M-circle dot. We find a total mass of 8400 M-circle dot for all BGPS sources in the Gemini OB1 molecular cloud, representing 6.5% of the cloud mass. By comparing the millimeter isothermal mass to the virial mass calculated from the NH3 line widths within a radius equal to the millimeter source size, we find a mean virial parameter (M-vir/M-iso) of 1.0 +/- 0.9 for the sample. We find mean values for the distributions of column densities of 1.0 x 10(22) cm(-2) for H-2, and 3.0 x 10(14) cm(-2) for NH3, giving a mean NH3 abundance of 3.0 x 10(-8) relative to H-2. We find volume-averaged densities on the order of 10(3)-10(4) cm(-3). The sizes and densities suggest that in the Gem OB1 region the BGPS is detecting the clumps from which stellar clusters form, rather than smaller, higher density cores where single stars or small multiple systems form.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. VII. Characterizing The Properties Of Massive Star-Forming Regions(2011-11) Dunham, Miranda K.; Rosolowsky, Erik; Evans, Neal J.; Cyganowski, Claudia; Urquhart, James S.; Dunham, Miranda K.; Evans, Neal J.We present the results of a Green Bank Telescope survey of NH(3)(1,1), (2,2), (3,3) lines toward 631 Bolocam Galactic Plane Survey (BGPS) sources at a range of Galactic longitudes in the inner Galaxy. We have detected the NH(3)(1,1) line toward 72% of our targets (456), demonstrating that the high column density features identified in the BGPS and other continuum surveys accurately predict the presence of dense gas. We have determined kinematic distances and resolved the distance ambiguity for all BGPS sources detected in NH(3). The BGPS sources trace the locations of the Scutum and Sagittarius spiral arms, with the number of sources peaking between R(Gal) similar to 4 and 5 kpc. We measure the physical properties of each source and find that depending on the distance, BGPS sources are primarily clumps, with some cores and clouds. We have examined the physical properties as a function of Galactocentric distance, and find a mean gas kinetic temperature of 15.6 K, and that the NH(3) column density and abundance decrease by nearly an order of magnitude between R(Gal) similar to 3 and 11 kpc. Comparing sources at similar distances demonstrates that the physical properties are indistinguishable, which suggests a similarity in clump structure across the Galactic disk. We have also compared the BGPS sources to criteria for efficient star formation presented independently by Heiderman et al. and Lada et al., and for massive star formation presented by Kauffmann et al. Forty-eight percent of our sample should be forming stars (including massive stars) with high efficiency, and 87% contain subregions that should be efficiently forming stars. Indeed, we find that 67% of the sample exhibit signs of star formation activity based on an association with a mid-infrared source.Item The Bolocam Galactic Plane Survey. VIII. A Mid-Infrared Kinematic Distance Discrimination Method(2013-06) Ellsworth-Bowers, Timothy P.; Glenn, Jason; Rosolowsky, Erik; Mairs, Steven; Evans, Neal J.; Battersby, Cara; Ginsburg, Adam; Shirley, Yancy L.; Bally, John; Evans, Neal J.We present a new distance estimation method for dust-continuum-identified molecular cloud clumps. Recent (sub-)millimeter Galactic plane surveys have cataloged tens of thousands of these objects, plausible precursors to stellar clusters, but detailed study of their physical properties requires robust distance determinations. We derive Bayesian distance probability density functions (DPDFs) for 770 objects from the Bolocam Galactic Plane Survey in the Galactic longitude range 7 degrees.5 <= l <= 65 degrees.. The DPDF formalism is based on kinematic distances, and uses any number of external data sets to place prior distance probabilities to resolve the kinematic distance ambiguity (KDA) for objects in the inner Galaxy. We present here priors related to the mid-infrared absorption of dust in dense molecular regions and the distribution of molecular gas in the Galactic disk. By assuming a numerical model of Galactic mid-infrared emission and simple radiative transfer, we match the morphology of (sub-) millimeter thermal dust emission with mid-infrared absorption to compute a prior DPDF for distance discrimination. Selecting objects first from (sub-) millimeter source catalogs avoids a bias towards the darkest infrared dark clouds (IRDCs) and extends the range of heliocentric distance probed by mid-infrared extinction and includes lower-contrast sources. We derive well-constrained KDA resolutions for 618 molecular cloud clumps, with approximately 15% placed at or beyond the tangent distance. Objects with mid-infrared contrast sufficient to be cataloged as IRDCs are generally placed at the near kinematic distance. Distance comparisons with Galactic Ring Survey KDA resolutions yield a 92% agreement. A face-on view of the Milky Way using resolved distances reveals sections of the Sagittarius and Scutum-Centaurus Arms. This KDA-resolution method for large catalogs of sources through the combination of (sub-) millimeter and mid-infrared observations of molecular cloud clumps is generally applicable to other dust-continuum Galactic plane surveys.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: Lambda = 1.1 And 0.35 Mm Dust Continuum Emission In The Galactic Center Region(2010-09) Bally, John; Aguirre, James; Battersby, Cara; Bradley, Eric Todd; Cyganowski, Claudia; Dowell, Darren; Drosback, Meredith; Dunham, Miranda K.; Evans, Neal J.; Ginsburg, Adam; Glenn, Jason; Harvey, Paul; Mills, Elisabeth; Merello, Manuel; Rosolowsky, Erik; Schlingman, Wayne; Shirley, Yancy L.; Stringfellow, Guy S.; Walawender, Josh; Williams, Jonathan; Dunham, Miranda K.; Evans, Neal J.; Merello, ManuelThe Bolocam Galactic Plane Survey (BGPS) data for a 6 deg(2) region of the Galactic plane containing the Galactic center are analyzed and compared to infrared and radio continuum data. The BGPS 1.1 mm emission consists of clumps interconnected by a network of fainter filaments surrounding cavities, a few of which are filled with diffuse near-IR emission indicating the presence of warm dust or with radio continuum characteristic of H II regions or supernova remnants. New 350 mu m images of the environments of the two brightest regions, Sgr A and B, are presented. Sgr B2 is the brightest millimeter-emitting clump in the Central Molecular Zone (CMZ) and may be forming the closest analog to a super star cluster in the Galaxy. The CMZ contains the highest concentration of millimeter- and submillimeter-emitting dense clumps in the Galaxy. Most 1.1 mm features at positive longitudes are seen in silhouette against the 3.6-24 mu m background observed by the Spitzer Space Telescope. However, only a few clumps at negative longitudes are seen in absorption, confirming the hypothesis that positive longitude clumps in the CMZ tend to be on the near side of the Galactic center, consistent with the suspected orientation of the central bar in our Galaxy. Some 1.1 mm cloud surfaces are seen in emission at 8 mu m, presumably due to polycyclic aromatic hydrocarbons. A similar to 0 degrees.2 (similar to 30 pc) diameter cavity and infrared bubble between l approximate to 0 degrees.0 and 0 degrees.2 surround the Arches and Quintuplet clusters and Sgr A. The bubble contains several clumpy dust filaments that point toward Sgr A*; its potential role in their formation is explored. Bania's Clump 2, a feature near l = 3 degrees-3 degrees.5 which exhibits extremely broad molecular emission lines (Delta V > 150 km s(-1)), contains dozens of 1.1 mm clumps. These clumps are deficient in near-and mid-infrared emission in the Spitzer images when compared to both the inner Galactic plane and the CMZ. Thus, Bania's Clump 2 is either inefficient in forming stars or is in a pre-stellar phase of clump evolution. The Bolocat catalog of 1.1 mm clumps contains 1428 entries in the Galactic center between l = 358 degrees.5 and l = 4 degrees.5 of which about 80% are likely to be within about 500 pc of the center. The mass spectrum above about 80 M(circle dot) can be described by a power-law Delta N/Delta M = N(0)M(-2.14(+ 0.1,-0.4)). The power-law index is somewhat sensitive to systematic grain temperature variations, may be highly biased by source confusion, and is very sensitive to the spatial filtering inherent in the data acquisition and reduction.Item The c2d Spitzer Spectroscopic Survey Of Ices Around Low-Mass Young Stellar Objects. II. CO2(2008-05) Pontoppidan, Klaus M.; Boogert, Adwin C. A.; Fraser, Helen J.; van Dishoeck, Ewine F.; Blake, Geoffrey A.; Lahuis, Fred; Oberg, Karin I.; Evans, Neal J.; Salyk, Colette; Evans, Neal J.This paper presents Spitzer IRS lambda/Delta lambda similar to 600 spectroscopy of the CO2 15.2 mu m bending mode toward 50 embedded young low-mass stars, taken mostly from the "Cores to Disks'' (c2d) Legacy program. The average abundance of solid CO2 relative to water in low-mass protostellar envelopes is 0.32 +/- 0.02, significantly higher than that found in quiescent molecular clouds and in massive star-forming regions. A decomposition of the observed CO2 bending mode profiles requires a minimum of five unique components. Roughly 2/3 of the CO2 ice is found in a water-rich environment, while most of the remaining 1/3 is found in a CO environment with strongly varying relative concentrations of CO2 to CO along each line of sight. Ground-based observations of solid CO toward a large subset of the c2d sample are used to further constrain the CO2:CO component and suggest a model in which low-density clouds form the CO2:H2O component and higher density clouds form the CO2:CO ice during and after the freezeout of gas-phase CO. The abundance of the CO2:CO component is consistent with cosmic-ray processing of the CO-rich part of the ice mantles, although a more quiescent formation mechanism is not ruled out. It is suggested that the subsequent evolution of the CO2 and CO profiles toward low-mass protostars, in particular the splitting of the CO2 bending mode due to pure, crystalline CO2, is first caused by distillation of the CO2:CO component through evaporation of CO due to thermal processing to similar to 20-30 K. The formation of pure CO2 via segregation from the H2O rich mantle may contribute to the band splitting at higher levels of thermal processing (greater than or similar to 50 K) but is harder to reconcile with the physical structure of protostellar envelopes around low-luminosity objects.Item Dust And The Type II-Plateau Supernova 2004dj(2011-05) Meikle, W. P. S.; Kotak, R.; Farrah, D.; Mattila, S.; Van Dyk, S. D.; Andersen, A. C.; Fesen, R.; Filippenko, Alexei V.; Foley, Ryan J.; Fransson, C.; Gerardy, C. L.; Hoflich, Peter A.; Lundqvist, P.; Pozzo, M.; Sollerman, Jesper; Wheeler, J. Craig; heeler, J. CraigWe present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN 2004dj, obtained with the Spitzer Space Telescope, spanning 106-1393 days after explosion. MIR photometry plus optical/near-IR observations are also reported. An early-time MIR excess is attributed to emission from non-silicate dust formed within a cool dense shell (CDS). Most of the CDS dust condensed between 50 days and 165 days, reaching a mass of 0.3 x 10(-5) M-circle dot. Throughout the observations, much of the longer wavelength (> 10 mu m) part of the continuum is explained as an IR echo from interstellar dust. The MIR excess strengthened at later times. We show that this was due to thermal emission from warm, non-silicate dust formed in the ejecta. Using optical/near-IR line profiles and the MIR continua, we show that the dust was distributed as a disk whose radius appeared to be shrinking slowly. The disk radius may correspond to a grain destruction zone caused by a reverse shock which also heated the dust. The dust-disk lay nearly face-on, had high opacities in the optical/near-IR regions, but remained optically thin in the MIR over much of the period studied. Assuming a uniform dust density, the ejecta dust mass by 996 days was (0.5 +/- 0.1) x 10(-4) M-circle dot and exceeded 10(-4) M-circle dot by 1393 days. For a dust density rising toward the center the limit is higher. Nevertheless, this study suggests that the amount of freshly synthesized dust in the SN 2004dj ejecta is consistent with that found from previous studies and adds further weight to the claim that such events could not have been major contributors to the cosmic dust budget.Item Dust And The Type II-Plateau Supernova 2004et(2009-10) Kotak, R.; Meikle, W. P. S.; Farrah, D.; Gerardy, C. L.; Foley, Ryan J.; Van Dyk, S. D.; Fransson, C.; Lundqvist, P.; Sollerman, Jesper; Fesen, R.; Filippenko, Alexei V.; Mattila, S.; Silverman, Jeffrey M.; Andersen, A. C.; Hoflich, Peter A.; Pozzo, M.; Wheeler, J. Craig; Wheeler, J. CraigWe present mid-infrared (MIR) observations of the Type II-plateau supernova (SN) 2004et, obtained with the Spitzer Space Telescope between 64 and 1406 days past explosion. Late-time optical spectra are also presented. For the period 300-795 days past explosion, we argue that the spectral energy distribution (SED) of SN 2004et comprises (1) a hot component due to emission from optically thick gas, as well as free-bound radiation; (2) a warm component due to newly formed, radioactively heated dust in the ejecta; and (3) a cold component due to an IR echo from the interstellar-medium dust of the host galaxy, NGC 6946. There may also have been a small contribution to the IR SED due to free-free emission from ionized gas in the ejecta. We reveal the first-ever spectroscopic evidence for silicate dust formed in the ejecta of a supernova. This is supported by our detection of a large, but progressively declining, mass of SiO. However, we conclude that the mass of directly detected ejecta dust grew to no more than a few times 10(-4) M(circle dot). We also provide evidence that the ejecta dust formed in comoving clumps of fixed size. We argue that, after about two years past explosion, the appearance of wide, box-shaped optical line profiles was due to the impact of the ejecta on the progenitor circumstellar medium and that the subsequent formation of a cool, dense shell was responsible for a later rise in the MIR flux. This study demonstrates the rich, multifaceted ways in which a typical core-collapse supernova and its progenitor can produce and/or interact with dust grains. The work presented here adds to the growing number of studies that do not support the contention that SNe are responsible for the large mass of observed dust in high-redshift galaxies.Item Dust Around R Coronae Borealis Stars. I. Spitzer/Infrared Spectrograph Observations(2011-09) Garcia-Hernandez, D. Anibal; Rao, N. Kameswara; Lambert, David L.; Lambert, David L.Spitzer/infrared spectrograph (IRS) spectra from 5 to 37 mu m for a complete sample of 31 R Coronae Borealis stars (RCBs) are presented. These spectra are combined with optical and near-infrared photometry of each RCB at maximum light to compile a spectral energy distribution (SED). The SEDs are fitted with blackbody flux distributions and estimates are made of the ratio of the infrared flux from circumstellar dust to the flux emitted by the star. Comparisons for 29 of the 31 stars are made with the Infrared Astronomical Satellite (IRAS) fluxes from three decades earlier: Spitzer and IRAS fluxes at 12 mu m and 25 mu m are essentially equal for all but a minority of the sample. For this minority, the IRAS to Spitzer flux ratio exceeds a factor of three. The outliers are suggested to be stars where formation of a dust cloud or dust puff is a rare event. A single puff ejected prior to the IRAS observations may have been reobserved by Spitzer as a cooler puff at a greater distance from the RCB. RCBs which experience more frequent optical declines have, in general, a circumstellar environment containing puffs subtending a larger solid angle at the star and a quasi-constant infrared flux. Yet, the estimated subtended solid angles and the blackbody temperatures of the dust show a systematic evolution to lower solid angles and cooler temperatures in the interval between IRAS and Spitzer. Dust emission by these RCBs and those in the LMC is similar in terms of total 24 mu m luminosity and [8.0]-[24.0] color index.Item Dust Around R Coronae Borealis Stars. II. Infrared Emission Features In An H-Poor Environment(2013-08) Garcia-Hernandez, D. Anibal; Rao, N. Kameswara; Lambert, David L.; Rao, N. Kameswara; Lambert, David L.Residual Spitzer/Infrared Spectrograph spectra for a sample of 31 R Coronae Borealis (RCB) stars are presented and discussed in terms of narrow emission features superimposed on the quasi-blackbody continuous infrared emission. A broad similar to 6-10 mu m dust emission complex is seen in the RCBs showing an extreme H-deficiency. A secondary and much weaker similar to 11.5-15 mu m broad emission feature is detected in a few RCBs with the strongest similar to 6-10 mu m dust complex. The Spitzer infrared spectra reveal for the first time the structure within the similar to 6-10 mu m dust complex, showing the presence of strong C-C stretching modes at similar to 6.3 and 8.1 mu m as well as of other dust features at similar to 5.9, 6.9, and 7.3 mu m, which are attributable to amorphous carbonaceous solids with little or no hydrogen. The few RCBs with only moderate H-deficiencies display the classical "unidentified infrared bands (UIRs)" and mid-infrared features from fullerene-related molecules. In general, the characteristics of the RCB infrared emission features are not correlated with the stellar and circumstellar properties, suggesting that the RCB dust features may not be dependent on the present physical conditions around RCB stars. The only exception seems to be the central wavelength of the 6.3 mu m feature, which is blueshifted in those RCBs showing also the UIRs, i.e., the RCBs with the smallest H deficiency.Item Evidence For A Correlation Between The Si II Lambda 4000 Width And Type Ia Supernova Color(2011-06) Nordin, Jakob; Ostman, Linda; Goobar, Ariel; Balland, C.; Lampeitl, Hubert; Nichol, Robert C.; Sako, Masao; Schneider, Donald P.; Smith, Mathew; Sollerman, Jesper; Wheeler, J. Craig; Wheeler, J. CraigWe study the pseudo-equivalent width of the Si II lambda 4000 feature of Type Ia supernovae (SNe Ia) in the redshift range 0.0024 <= z <= 0.634. We find that this spectral indicator correlates with the light curve color excess (SALT2c) as well as previously defined spectroscopic subclasses (Branch types) and the evolution of the Si II lambda 6150 velocity, i.e., the so-called velocity gradient. Based on our study of 55 objects from different surveys, we find indications that the Si II lambda 4000 spectral indicator could provide important information to improve cosmological distance measurements with SNe Ia.Item Evidence For Type Ia Supernova Diversity From Ultraviolet Observations With The Hubble Space Telescope(2012-04) Wang, Xiaofeng; Wang, Lifan; Filippenko, Alexei V.; Baron, Eddie; Kromer, Markus; Jack, Dennis; Zhang, Tianmeng; Aldering, Greg; Antilogus, Pierre; Arnett, W. David; Baade, Dietrich; Barris, Brian J.; Benetti, Stefano; Bouchet, Patrice; Burrows, Adam S.; Canal, Ramon; Cappellaro, Enrico; Carlberg, Raymond G.; di Carlo, Elisa; Challis, Peter J.; Crotts, Arlin P. S.; Danziger, John I.; Della Valle, Massimo; Fink, Michael; Foley, Ryan J.; Fransson, Claes; Gal-Yam, Avishay; Garnavich, Peter M.; Gerardy, Chris L.; Goldhaber, Gerson; Hamuy, Mario; Hillebrandt, Wolfgang; Hoeflich, Peter; Holland, Stephen T.; Holz, Daniel E.; Hughes, John P.; Jeffery, David J.; Jha, Saurabh W.; Kasen, Dan; Khokhlov, Alexei M.; Kirshner, Robert P.; Knop, Robert A.; Kozma, Cecilia; Krisciunas, Kevin; Lee, Brian C.; Leibundgut, Bruno; Lentz, Eric J.; Leonard, Douglas C.; Lewin, Walter H. G.; Li, Weidong; Livio, Mario; Lundqvist, Peter; Maoz, Dan; Matheson, Thomas; Mazzali, Paolo A.; Meikle, Peter; Miknaitis, Gajus; Milne, Peter A.; Mochnacki, Stefan W.; Nomoto, Ken'ichi; Nugent, Peter E.; Oran, Elaine S.; Panagia, Nino; Perlmutter, Saul; Phillips, Mark M.; Pinto, Philip; Poznanski, Dovi; Pritchet, Christopher J.; Reinecke, Martin; Riess, Adam G.; Ruiz-Lapuente, Pilar; Scalzo, Richard A.; Schlegel, Eric M.; Schmidt, Brian P.; Siegrist, James; Soderberg, Alicia M.; Sollerman, Jesper; Sonneborn, George; Spadafora, Anthony; Spyromilio, Jason; Sramek, Richard A.; Starrfield, Sumner G.; Strolger, Louis G.; Suntzeff, Nicholas B.; Thomas, Rollin C.; Tonry, John L.; Tornambe, Amedeo; Truran, James W.; Turatto, Massimo; Turner, Michael; Van Dyk, Schuyler D.; Weiler, Kurt W.; Wheeler, J. Craig; Wood-Vasey, Michael; Woosley, Stanford E.; Yamaoka, Hitoshi; Wheeler, J. CraigWe present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This data set provides unique spectral time series down to 2000 angstrom. Significant diversity is seen in the near-maximum-light spectra (similar to 2000-3500 angstrom) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminositiesmeasured in the uvw1/F250W filter are found to correlate with the B-band light-curve shape parameter Delta m(15)(B), but with much larger scatter relative to the correlation in the broadband B band (e.g., similar to 0.4 mag versus similar to 0.2 mag for those with 0.8 mag < Delta m(15)(B) < 1.7 mag). SN 2004dt is found as an outlier of this correlation (at > 3 sigma), being brighter than normal SNe Ia such as SN 2005cf by similar to 0.9 mag and similar to 2.0 mag in the uvw1/F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effects.Item Extinction Maps Toward The Milky Way Bulge: Two-Dimensional And Three-Dimensional Tests With APOGEE(2014-07) Schultheis, M.; Zasowski, G.; Prieto, C. A.; Anders, F.; Beaton, R. L.; Beers, T. C.; Bizyaev, D.; Chiappini, C.; Frinchaboy, P. M.; Perez, A. E. G.; Ge, J.; Hearty, F.; Holtzman, J.; Majewski, S. R.; Muna, D.; Nidever, D.; Shetrone, M.; Schneider, D. P.; Shetrone, Matthew D.Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable extinction measures and distances for a large number of stars that are independent of these maps, tests of their accuracy and systematics have been limited. Our goal is to assess a variety of photometric stellar extinction estimates, including both two-dimensional and three-dimensional extinction maps, using independent extinction measures based on a large spectroscopic sample of stars toward the Milky Way bulge. We employ stellar atmospheric parameters derived from high-resolution H-band Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra, combined with theoretical stellar isochrones, to calculate line-of-sight extinction and distances for a sample of more than 2400 giants toward the Milky Way bulge. We compare these extinction values to those predicted by individual near-IR and near+mid-IR stellar colors, two-dimensional bulge extinction maps, and three-dimensional extinction maps. The long baseline, near+mid-IR stellar colors are, on average, the most accurate predictors of the APOGEE extinction estimates, and the two-dimensional and three-dimensional extinction maps derived from different stellar populations along different sightlines show varying degrees of reliability. We present the results of all of the comparisons and discuss reasons for the observed discrepancies. We also demonstrate how the particular stellar atmospheric models adopted can have a strong impact on this type of analysis, and discuss related caveats.Item The Gould Belt "Misfits" Survey: The Real Solar Neighborhood Protostars(2015-06) Heiderman, Amanda; Evans, Neal J.; Evans, Neal J.We present an HCO+ J = 3. 2 survey of Class 0+I and Flat SED young stellar objects (YSOs) found in the Gould Belt clouds by surveys with Spitzer. Our goal is to provide a uniform Stage 0+I source indicator for these embedded protostar candidates. We made single point HCO+J = 3 -> 2 measurements toward the source positions at the CSO and APEX of 546 YSOs (89% of the Class 0+I +Flat SED sample). Using the criteria from van Kempen et al., we classify sources as Stage 0+I or bona fide protostars and find that 84% of detected sources meet the criteria. We recommend a timescale for the evolution of Stage 0+I (embedded protostars) of 0.54 Myr. We find significant correlations of HCO+integrated intensity with a and Tbol but not with Lbol. The detection fraction increases smoothly as a function of a and Lbol, while decreasing smoothly with Tbol. Using the Stage 0+I sources tightens the relation between protostars and high extinction regions of the cloud; 89% of Stage I sources lie in regions with A(V) > 8 mag. Class 0+I and Flat SED YSOs that are not detected in HCO+ have, on average, a factor of similar to 2 higher Tbol and a factor of similar to 5 lower L-bol than YSOs with HCO+ detections. We find less YSO contamination, defined as the number of undetected YSOs divided by the total number surveyed, for sources with T-bol less than or similar to 600 K and L-bol greater than or similar to 1 L-circle dot. The contamination percentage is > 90% at A(V) < 4 mag and decreases as A(V) increases.Item GRB 090417B And Its Host Galaxy: A Step Toward An Understanding Of Optically Dark Gamma-Ray Bursts(2010-07) Holland, Steven T.; Sbarufatti, Boris; Shen, Rongfeng; Schady, Patricia; Cummings, Jay R.; Fonseca, Emmanuel; Fynbo, Johan P. U.; Jakobsson, Pall; Leitet, Elisabet; Linne, Staffan; Roming, Peter W. A.; Still, Martin; Zhang, Bing; Shen, RongfengGRB 090417B was an unusually long burst with a T(90) duration of at least 2130 s and a multi-peaked light curve at energies of 15-150 keV. It was optically dark and has been associated with a bright star-forming galaxy at a redshift of 0.345 that is broadly similar to the Milky Way. This is one of the few cases where a host galaxy has been clearly identified for a dark gamma-ray burst (GRB) and thus an ideal candidate for studying the origin of dark bursts. We find that the dark nature of GRB 090417B cannot be explained by high redshift, incomplete observations, or unusual physics in the production of the afterglow. Assuming the standard relativistic fireball model for the afterglow we find that the optical flux is at least 2.5 mag fainter than predicted by the X-ray flux. The Swift/XRT X-ray data are consistent with the afterglow being obscured by a dense, localized sheet of dust approximately 30-80 pc from the burst along the line of sight. Our results suggest that this dust sheet imparts an extinction of A(V) greater than or similar to 12 mag, which is sufficient to explain the missing optical flux. GRB 090417B is an example of a GRBs that is dark due to the localized dust structure in its host galaxy.Item The HETDEX Pilot Survey. II. The Evolution Of The Ly Alpha Escape Fraction From The Ultraviolet Slope And Luminosity Function Of 1.9 < Z < 3.8 Laes(2011-07) Blanc, Guillermo A.; Adams, Joshua J.; Gebhardt, Karl; Hill, Gary J.; Drory, Niv; Hao, Lei; Bender, Ralf; Ciardullo, Robin; Finkelstein, Steven L.; Fry, Alexander B.; Gawiser, Eric; Gronwall, Caryl; Hopp, Ulrich; Jeong, Donghui; Kelzenberg, Ralf; Komatsu, Eiichiro; MacQueen, Phillip; Murphy, Jeremy D.; Roth, Martin M.; Schneider, Donald P.; Tufts, Joseph; Blanc, Guillermo A.; Adams, Joshua J.; Gebhardt, Karl; Hill, Gary J.; Fry, Alexander B.; |Jeong, Donghui; Komatsu, Eiichiro; Murphy, Jeremy D.We study the escape of Ly alpha photons from Ly alpha emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9 < z < 3.8 detected through integral-field spectroscopy of blank fields by The Hobby Eberly Telescope Dark Energy Experiment Pilot Survey. For 89 LAEs with broadband counterparts we measure ultraviolet (UV) luminosities and UV slopes, and estimate E(B - V) under the assumption of a constant intrinsic UV slope for LAEs. These quantities are used to estimate dust-corrected star formation rates (SFRs). Comparison between the observed Ly alpha luminosity and that predicted by the dust-corrected SFR yields the Ly alpha escape fraction. We also measure the Ly alpha luminosity function and luminosity density (rho(Ly alpha)) at 2 < z < 4. Using this and other measurements from the literature at 0.3 < z < 7.7 we trace the redshift evolution of rho(Ly alpha). We compare it to the expectations from the star formation history of the universe and characterize the evolution of the Ly alpha escape fraction of galaxies. LAEs at 2 < z < 4 selected down to a luminosity limit of L(Ly alpha) > (3-6) x 10(42) erg s(-1) (0.25-0.5 L*), have a mean < E(B - V)> = 0.13 +/- 0.01, implying an attenuation of similar to 70% in the UV. They show a median UV uncorrected SFR = 11 M-circle dot yr(-1), dust-corrected SFR = 34 M-circle dot yr(-1), and Ly alpha equivalent widths (EWs) which are consistent with normal stellar populations. We measure a median Ly alpha escape fraction of 29%, with a large scatter and values ranging from a few percent to 100%. The Ly alpha escape fraction in LAEs correlates with E(B - V) in a way that is expected if Ly alpha photons suffer from similar amounts of dust extinction as UV continuum photons. This result implies that a strong enhancement of the Ly alpha EW with dust, due to a clumpy multi-phase interstellar medium (ISM), is not a common process in LAEs at these redshifts. It also suggests that while in other galaxies Ly alpha can be preferentially quenched by dust due to its scattering nature, this is not the case in LAEs. We find no evolution in the average dust content and Ly alpha escape fraction of LAEs from z similar to 4 to 2. We see hints of a drop in the number density of LAEs from z similar to 4 to 2 in the redshift distribution and the Ly alpha luminosity function, although larger samples are required to confirm this. The mean Ly alpha escape fraction of the overall galaxy population decreases significantly from z similar to 6 to z similar to 2, in agreement with recent results. Our results point toward a scenario in which star-forming galaxies build up significant amounts of dust in their ISM between z similar to 6 and 2, reducing their Ly alpha escape fraction, with LAE selection preferentially detecting galaxies which have the highest escape fractions given their dust content. The fact that a large escape of Ly alpha photons is reached by z similar to 6 implies that better constraints on this quantity at higher redshifts might detect re-ionization in a way that is uncoupled from the effects of dust.Item High-Resolution Optical Spectroscopy of DY Cen: Diffuse Interstellar Bands in a Proto-Fullerene Circumstellar Environment?(2012-11) Garcia-Hernandez, D. A.; Rao, N. Kameswara; Lambert, David L.; Rao, N. Kameswara; Lambert, David L.We search high-resolution and high-quality VLT/UVES optical spectra of the hot R Coronae Borealis star DY Cen for electronic transitions of the C-60 molecule and diffuse interstellar bands (DIBs). We report the non-detection of the strongest C-60 electronic transitions (e. g., those at similar to 3760, 3980, and 4024 angstrom). The absence of C-60 absorption bands may support recent laboratory results, which show that the similar to 7.0, 8.5, 17.4, and 18.8 mu m emission features seen in DY Cen-and other similar objects with polycyclic-aromatic-hydrocarbon-like dominated IR spectra-are attributable to proto-fullerenes or fullerene precursors rather than to C-60. DIBs toward DY Cen are normal for its reddening; the only exception is the DIB at 6284 angstrom (possibly also the 7223 angstrom DIB) which is found to be unusually strong. We also report the detection of a new broad (FWHM similar to 2 angstrom) and unidentified feature centered at similar to 4000 angstrom. We suggest that this new band may be related to the circumstellar proto-fullerenes seen at infrared wavelengths.