Showing papers by "Joseph L. Hora published in 2010"
TL;DR: In this article, a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties.
Abstract: We present a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE-SMC survey database, for which we present uniform photometry from 0.3to24 {mu}m in the UBVIJHK{sub s} +IRAC+MIPS24 bands. We compare the color-magnitude diagrams and color-color diagrams to those of stars in the Large Magellanic Cloud (LMC), finding that the brightest infrared sources in the SMC are also the red supergiants, supergiant B[e] (sgB[e]) stars, luminous blue variables, and Wolf-Rayet stars, with the latter exhibiting less infrared excess, the red supergiants being less dusty and the sgB[e] stars being on average less luminous. Among the objects detected at 24 {mu}m in the SMC are a few very luminous hypergiants, four B-type stars with peculiar, flat spectral energy distributions, and all three known luminous blue variables. We detect a distinct Be star sequence, displaced to the red, and suggest a novel method of confirming Be star candidates photometrically. We find a higher fraction of Oe and Be starsmore » among O and early-B stars in our SMC catalog, respectively, when compared to the LMC catalog, and that the SMC Be stars occur at higher luminosities. We estimate mass-loss rates for the red supergiants, confirming the correlation with luminosity even at the metallicity of the SMC. Finally, we confirm the new class of stars displaying composite A and F type spectra, the sgB[e] nature of 2dFS1804 and find the F0 supergiant 2dFS3528 to be a candidate luminous blue variable with cold dust.« less
190 citations
Space Telescope Science Institute1, Smithsonian Astrophysical Observatory2, Harvard University3, University of Arizona4, Hoffmann-La Roche5, University of Maryland, College Park6, University of Strasbourg7, University of Wisconsin-Madison8, Johns Hopkins University9, Louisiana State University10, National Radio Astronomy Observatory11, Nagoya University12, Swinburne University of Technology13, Leiden University14, University of Manchester15, Sejong University16, University of Missouri17, Iowa State University18, University College London19, Keele University20, Osaka Prefecture University21, California Institute of Technology22, Max Planck Society23, Universities Space Research Association24, University of Chile25, Carnegie Institution for Science26, Centre national de la recherche scientifique27, Space Science Institute28
TL;DR: In this paper, the authors used the Herschel Space Observatory's PACS and SPIRE photometry cameras to image a 2° × 8° strip through the Large and Small Magellanic Clouds (LMC and SMC) at a position angle of 22.5°.
Abstract: The HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) of the Magellanic Clouds will use dust emission to investigate the life cycle of matter in both the Large and Small Magellanic Clouds (LMC and SMC). Using the Herschel Space Observatory’s PACS and SPIRE photometry cameras, we imaged a 2° × 8° strip through the LMC, at a position angle of ~22.5° as part of the science demonstration phase of the Herschel mission. We present the data in all 5 Herschel bands: PACS 100 and 160 μm and SPIRE 250, 350 and 500 μm. We present two dust models that both adequately fit the spectral energy distribution for the entire strip and both reveal that the SPIRE 500 μm emission is in excess of the models by ~6 to 17%. The SPIRE emission follows the distribution of the dust mass, which is derived from the model. The PAH-to-dust mass (f_(PAH)) image of the strip reveals a possible enhancement in the LMC bar in agreement with previous work. We compare the gas mass
distribution derived from the HI 21 cm and CO J = 1−0 line emission maps to the dust mass map from the models and derive gas-to-dust mass ratios (GDRs). The dust model, which uses the standard graphite and silicate optical properties for Galactic dust, has a very low GDR = 65^(+15)
_(−18) making it an unrealistic dust model for the LMC. Our second dust model, which uses amorphous carbon instead of graphite, has a flatter emissivity index in the submillimeter and results in a GDR = 287^_(+25)_(−42) that is more consistent with a GDR inferred from extinction.
145 citations
TL;DR: In this article, a method to discriminate submillimeter cores found by Submillimeter Common-User Bolometer Array (SCUBA) as starless or protostellar, using point source photometry from Spitzer wide field surveys was developed.
Abstract: Using data from the SCUBA Legacy Catalogue (850 μm) and Spitzer Space Telescope (3.6-70 μm), we explore dense cores in the Ophiuchus, Taurus, Perseus, Serpens, and Orion molecular clouds. We develop a new method to discriminate submillimeter cores found by Submillimeter Common-User Bolometer Array (SCUBA) as starless or protostellar, using point source photometry from Spitzer wide field surveys. First, we identify infrared sources with red colors associated with embedded young stellar objects (YSOs). Second, we compare the positions of these YSO candidates to our submillimeter cores. With these identifications, we construct new, self-consistent starless and protostellar core mass functions (CMFs) for the five clouds. We find best-fit slopes to the high-mass end of the CMFs of –1.26 ± 0.20, –1.22 ± 0.06, –0.95 ± 0.20, and –1.67 ± 0.72 for Ophiuchus, Taurus, Perseus, and Orion, respectively. Broadly, these slopes are each consistent with the –1.35 power-law slope of the Salpeter initial mass function at higher masses, but suggest some differences. We examine a variety of trends between these CMF shapes and their parent cloud properties, potentially finding a correlation between the high-mass slope and core temperature. We also find a trend between core mass and effective size, but we are very limited by sensitivity. We make similar comparisons between core mass and size with visual extinction (for A_V ≥ 3) and find no obvious trends. We also predict the numbers and mass distributions of cores that future surveys with SCUBA-2 may detect in each of these clouds.
141 citations
TL;DR: In this article, the authors identify infrared sources with red colors associated with embedded young stellar objects (YSOs) and compare the positions of these YSO-candidates to our submillimeter cores.
Abstract: Using data from the SCUBA Legacy Catalogue (850 um) and Spitzer Space Telescope (3.6 - 70 um), we explore dense cores in the Ophiuchus, Taurus, Perseus, Serpens, and Orion molecular clouds. We develop a new method to discriminate submillimeter cores found by SCUBA as starless or protostellar, using point source photometry from Spitzer wide field surveys. First, we identify infrared sources with red colors associated with embedded young stellar objects (YSOs). Second, we compare the positions of these YSO-candidates to our submillimeter cores. With these identifications, we construct new, self-consistent starless and protostellar core mass functions (CMFs) for the five clouds. We find best fit slopes to the high-mass end of the CMFs of -1.26 +/- 0.20, -1.22 +/- 0.06, -0.95 +/- 0.20, and -1.67 +/- 0.72 for Ophiuchus, Taurus, Perseus, and Orion, respectively. Broadly, these slopes are each consistent with the -1.35 power-law slope of the Salpeter IMF at higher masses, but suggest some differences. We examine a variety of trends between these CMF shapes and their parent cloud properties, potentially finding a correlation between the high-mass slope and core temperature. We also find a trend between core mass and effective size, but we are very limited by sensitivity. We make similar comparisons between core mass and size with visual extinction (for A_V >= 3) and find no obvious trends. We also predict the numbers and mass distributions of cores that future surveys with SCUBA-2 may detect in each of these clouds.
131 citations
University of Manchester1, Iowa State University2, Hoffmann-La Roche3, Space Telescope Science Institute4, University of Missouri5, University of Virginia6, University of California, Berkeley7, University of Arizona8, Paris Diderot University9, Katholieke Universiteit Leuven10, California Institute of Technology11, Harvard University12, National Radio Astronomy Observatory13, Nagoya University14, University College London15, Imperial College London16, Keele University17, Max Planck Society18, Cornell University19, Johns Hopkins University20, Institut d'Astrophysique de Paris21, University of Toledo22, Space Science Institute23
TL;DR: The SAGE-Spec Spitzer Legacy program as discussed by the authors is a spectroscopic follow-up to the SAGE LMC photometric survey of the Large Magellanic Cloud carried out with the Spitzer Space Telescope.
Abstract: The SAGE-Spec Spitzer Legacy program is a spectroscopic follow-up to the SAGE-LMC photometric survey of the Large Magellanic Cloud carried out with the Spitzer Space Telescope. We present an overview of SAGE-Spec and some of its first results. The SAGE-Spec program aims to study the life cycle of gas and dust in the Large Magellanic Cloud and to provide information essential to the classification of the point sources observed in the earlier SAGE-LMC photometric survey. We acquired 224.6 h of observations using the infrared spectrograph and the spectral energy distribution (SED) mode of the Multiband Imaging Photometer for Spitzer. The SAGE-Spec data, along with archival Spitzer spectroscopy of objects in the Large Magellanic Cloud, are reduced and delivered to the community. We discuss the observing strategy, the specific data-reduction pipelines applied, and the dissemination of data products to the scientific community. Initial science results include the first detection of an extragalactic 21 mu m feature toward an evolved star and elucidation of the nature of disks around RV Tauri stars in the Large Magellanic Cloud. Toward some young stars, ice features are observed in absorption. We also serendipitously observed a background quasar, at a redshift of z approximate to 0.14, which appears to be hostless.
104 citations
Space Telescope Science Institute1, Smithsonian Astrophysical Observatory2, Harvard University3, University of Arizona4, Hoffmann-La Roche5, University of Maryland, College Park6, University of Strasbourg7, University of Wisconsin-Madison8, Johns Hopkins University9, Louisiana State University10, National Radio Astronomy Observatory11, Nagoya University12, Swinburne University of Technology13, Leiden University14, University of Manchester15, Sejong University16, University of Missouri17, Iowa State University18, University College London19, Keele University20, Osaka Prefecture University21, California Institute of Technology22, Max Planck Society23, Universities Space Research Association24, University of Chile25, Carnegie Institution for Science26, Centre national de la recherche scientifique27, Space Science Institute28
TL;DR: In this article, the authors presented two dust models that both adequately fit the spectral energy distribution for the entire strip and both reveal that the SPIRE 500 µm emission is in excess of the models by 6 to 17%.
Abstract: The HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) of the Magellanic Clouds will use dust emission to investigate the life cycle of matter in both the Large and Small Magellanic Clouds (LMC and SMC). Using the Herschel Space Observatory's PACS and SPIRE photometry cameras, we imaged a 2x8 square degree strip through the LMC, at a position angle of ~22.5 degrees as part of the science demonstration phase of the Herschel mission. We present the data in all 5 Herschel bands: PACS 100 and 160 {\mu}m and SPIRE 250, 350 and 500 {\mu}m. We present two dust models that both adequately fit the spectral energy distribution for the entire strip and both reveal that the SPIRE 500 {\mu}m emission is in excess of the models by 6 to 17%. The SPIRE emission follows the distribution of the dust mass, which is derived from the model. The PAH-to-dust mass (f_PAH) image of the strip reveals a possible enhancement in the LMC bar in agreement with previous work. We compare the gas mass distribution derived from the HI 21 cm and CO J=1-0 line emission maps to the dust mass map from the models and derive gas-to-dust mass ratios (GDRs). The dust model, which uses the standard graphite and silicate optical properties for Galactic dust, has a very low GDR = 65(+15,-18) making it an unrealistic dust model for the LMC. Our second dust model, which uses amorphous carbon instead of graphite, has a flatter emissivity index in the submillimeter and results in a GDR = 287(+25,-42) that is more consistent with a GDR inferred from extinction.
103 citations
TL;DR: The ExploreNEOs project as mentioned in this paper uses the Spitzer Space Telescope in its Warm Spitzer mode to study the history of near-Earth space by deriving the physical properties of a large number of asteroids.
Abstract: We have begun the ExploreNEOs project in which we observe some 700 Near-Earth Objects (NEOs) at 3.6 and 4.5 μm with the Spitzer Space Telescope in its Warm Spitzer mode. From these measurements and catalog optical photometry we derive albedos and diameters of the observed targets. The overall goal of our ExploreNEOs program is to study the history of near-Earth space by deriving the physical properties of a large number of NEOs. In this paper, we describe both the scientific and technical construction of our ExploreNEOs program. We present our observational, photometric, and thermal modeling techniques. We present results from the first 101 targets observed in this program. We find that the distribution of albedos in this first sample is quite broad, probably indicating a wide range of compositions within the NEO population. Many objects smaller than 1 km have high albedos (0.35), but few objects larger than 1 km have high albedos. This result is consistent with the idea that these larger objects are collisionally older, and therefore possess surfaces that are more space weathered and therefore darker, or are not subject to other surface rejuvenating events as frequently as smaller NEOs.
95 citations
TL;DR: In this paper, Chandra X-ray data of the NGC 1333 embedded cluster and combine these data with existing Chandra data, Spitzer photometry, and ground-based spectroscopy of both the Serpens cloud core clusters to perform a detailed study of the Xray properties of two of the nearest embedded clusters to the Sun.
Abstract: We present new Chandra X-ray data of the NGC 1333 embedded cluster and combine these data with existing Chandra data, Spitzer photometry, and ground-based spectroscopy of both the NGC 1333 and Serpens cloud core clusters to perform a detailed study of the X-ray properties of two of the nearest embedded clusters to the Sun. We first present new, deeper observations of NGC 1333 with Chandra ACIS-I and combine these with existing Spitzer observations of the region. In NGC 1333, a total of 95 cluster members are detected in X-rays of which 54 were previously identified in the Spitzer data. Of the Spitzer-identified sources, we detected 23% of the Class I protostars, 53% of the flat-spectrum sources, 52% of the Class II, and 50% of the transition disk young stellar objects (YSOs). Forty-one Class III members of the cluster are identified, bringing the total identified YSO population to 178. The X-ray luminosity functions (XLFs) of the NGC 1333 and Serpens clusters are compared to each other and the Orion Nebula Cluster (ONC). Based on a comparison of the XLFs of the Serpens and NGC 1333 clusters to the previously published ONC, we obtain a new distance for the Serpens cluster of 360+22 –13 pc. Using our previously published spectral types, effective temperatures, and bolometric luminosities, we analyze the dependence of the X-ray emission on the measured stellar properties. The X-ray luminosity was found to depend on the calculated bolometric luminosity as in previous studies of other clusters. We examine the dependence of LX on stellar surface area and effective temperature, and find that LX depends primarily on the stellar surface area. In the NGC 1333 cluster, the Class III sources have a somewhat higher X-ray luminosity for a given surface area. We also find evidence in NGC 1333 for a jump in the X-ray luminosity between spectral types of M0 and K7, we speculate that this may result from the presence of radiative zones in the K-stars. The gas column density versus extinction in the NGC 1333 parental molecular cloud was examined using the hydrogen column density determined from the X-ray absorption to the embedded stars and the K-band extinction measured to those stars. In NGC 1333, we find NH = 0.89 ± 0.13 × 1022 AK , this is lower than expected of the standard interstellar medium but similar to that found previously in the Serpens cloud core.
94 citations
University of California, Berkeley1, Harvard University2, Smith College3, University of Massachusetts Amherst4, University of Toledo5, University of Cologne6, Air Force Research Laboratory7, Boston College8, Cornell University9, Centro de Investigaciones de Astronomia10, University of Hertfordshire11
TL;DR: In this article, the authors proposed a method to solve the problem of the UHRA U-HRA standard for the detection of the Earth's magnetic field in a single image.
Abstract: Original article can be found at: http://iopscience.iop.org/0004-637X Copyright American Astronomical Society. [Full text of this article is not available in the UHRA]
85 citations
TL;DR: Using Spitzer IRAC observations from the SAGE-SMC Legacy program and archived SpitzerIRAC data, this paper investigated dust production in 47Tuc, a nearby massive Galactic globular cluster.
Abstract: Using Spitzer IRAC observations from the SAGE-SMC Legacy program and archived Spitzer IRAC data, we investigate dust production in 47Tuc, a nearby massive Galactic globular cluster. A previous study detected infrared excess, indicative of circumstellar dust, in a large population of stars in 47Tuc, spanning the entire Red Giant Branch (RGB). We show that those results suffered from effects caused by stellar blending and imaging artifacts and that it is likely that no stars below �1 mag from the tip of the RGB are producing dust. The only stars that appear to harbor dust are variable stars, which are also the coolest and most luminous stars in the cluster. Subject headings: circumstellar matter — globular clusters: individual (47Tuc) — infrared: stars — stars: AGB and post-AGB — stars: mass-loss — stars: winds, outflows
59 citations
TL;DR: In this paper, the authors use the Spitzer IRAC and MIPS bands to determine the monochromatic IR band that most accurately traces the bolometric IR flux (TIR), which can then be used to estimate an obscured SFR.
Abstract: HII regions are the birth places of stars, and as such they provide the best measure of current star formation rates (SFRs) in galaxies. The close proximity of the Magellanic Clouds allows us to probe the nature of these star forming regions at small spatial scales. We aim to determine the monochromatic IR band that most accurately traces the bolometric IR flux (TIR), which can then be used to estimate an obscured SFR. We present the spatial analysis, via aperture/annulus photometry, of 16 LMC and 16 SMC HII region complexes using the Spitzer IRAC and MIPS bands. UV rocket data and SHASSA H-alpha data are also included. We find that nearly all of the LMC and SMC HII region SEDs peak around 70um, from ~10 to ~400 pc from the central sources. As a result, the sizes of HII regions as probed by 70um is approximately equal to the sizes as probed by TIR (about 70 pc in radius); the radial profile of the 70um flux, normalized by TIR, is constant at all radii (70um ~ 0.45 TIR); the 1-sigma standard deviation of the 70um fluxes, normalized by TIR, is a lower fraction of the mean (0.05 to 0.12 out to ~220 pc) than the normalized 8, 24, and 160um normalized fluxes (0.12 to 0.52); and these results are invariant between the LMC and SMC. From these results, we argue that 70um is the most suitable IR band to use as a monochromatic obscured star formation indicator because it most accurately reproduces the TIR of HII regions in the LMC and SMC and over large spatial scales. We also explore the general trends of the 8, 24, 70, and 160um bands in the LMC and SMC HII region SEDs, radial surface brightness profiles, sizes, and normalized (by TIR) radial flux profiles. We derive an obscured SFR equation that is modified from the literature to use 70um luminosity, SFR(Mo/yr) = 9.7(0.7)x10^{-44} L(70)(ergs/s), which is applicable from 10 to 300 pc distance from the center of an HII region.
TL;DR: In this paper, the authors used the bolometric infrared flux (TIR) to estimate the star formation rate in the Magellanic Clouds and found that the TIR provides a measure of the obscured star formation because the UV photons from hot young stars are absorbed by dust and reemitted across the mid-to-far-infrared (IR) spectrum.
Abstract: H II regions are the birth places of stars, and as such they provide the best measure of current star formation rates (SFRs) in galaxies. The close proximity of the Magellanic Clouds allows us to probe the nature of these star forming regions at small spatial scales. To study the H II regions, we compute the bolometric infrared flux, or total infrared (TIR), by integrating the flux from 8 to 500 ?m. The TIR provides a measure of the obscured star formation because the UV photons from hot young stars are absorbed by dust and re-emitted across the mid-to-far-infrared (IR) spectrum. We aim to determine the monochromatic IR band that most accurately traces the TIR and produces an accurate obscured SFR over large spatial scales. We present the spatial analysis, via aperture/annulus photometry, of 16 Large Magellanic Cloud (LMC) and 16 Small Magellanic Cloud (SMC) H II region complexes using the Spitzer Space Telescope's IRAC (3.6, 4.5, 8 ?m) and MIPS (24, 70, 160 ?m) bands. Ultraviolet rocket data (1500 and 1900 ?) and SHASSA H? data are also included. All data are convolved to the MIPS 160 ?m resolution (40 arcsec full width at half-maximum), and apertures have a minimum radius of 35''. The IRAC, MIPS, UV, and H? spatial analysis are compared with the spatial analysis of the TIR. We find that nearly all of the LMC and SMC H II region spectral energy distributions (SEDs) peak around 70 ?m at all radii, from ~10 to ~400?pc from the central ionizing sources. As a result, we find the following: the sizes of H II regions as probed by 70 ?m are approximately equal to the sizes as probed by TIR (70?pc in radius); the radial profile of the 70 ?m flux, normalized by TIR, is constant at all radii (70 ?m ~ 0.45TIR); the 1? standard deviation of the 70 ?m fluxes, normalized by TIR, is a lower fraction of the mean (0.05-0.12 out to ~220?pc) than the normalized 8, 24, and 160 ?m normalized fluxes (0.12-0.52); and these results are the same for the LMC and the SMC. From these results, we argue that 70 ?m is the most suitable IR band to use as a monochromatic obscured star formation indicator because it most accurately reproduces the TIR of H II regions in the LMC and SMC and over large spatial scales. We also explore the general trends of the 8, 24, 70, and 160 ?m bands in the LMC and SMC H II region SEDs, radial surface brightness profiles, sizes, and normalized (by TIR) radial flux profiles. We derive an obscured SFR equation that is modified from the literature to use 70 ?m luminosity, SFR(M ? yr?1) = 9.7(0.7) ? 10?44 L 70(ergs s?1), which is applicable from 10 to 300?pc distance from the center of an H II region. We include an analysis of the spatial variations around H II regions between the obscured star formation indicators given by the IR and the unobscured star formation indicators given by UV and H?. We compute obscured and unobscured SFRs using equations from the literature and examine the spatial variations of the SFRs around H II regions.
TL;DR: Using Spitzer IRAC observations from the SAGE-SMC Legacy program and archived SpitzerIRAC data, this article investigated dust production in 47 Tuc, a nearby massive Galactic globular cluster.
Abstract: Using Spitzer IRAC observations from the SAGE-SMC Legacy program and archived Spitzer IRAC data, we investigate dust production in 47 Tuc, a nearby massive Galactic globular cluster. A previous study detected infrared excess, indicative of circumstellar dust, in a large population of stars in 47 Tuc, spanning the entire Red Giant Branch (RGB). We show that those results suffered from effects caused by stellar blending and imaging artifacts and that it is likely that no stars below about 1 mag from the tip of the RGB are producing dust. The only stars that appear to harbor dust are variable stars, which are also the coolest and most luminous stars in the cluster.
TL;DR: In this article, the authors report an unexpected variability among mid-infrared spectra (IRTF and Spitzer data) of eight S-type asteroids for which all other remote sensing interpretations (e.g., VNIR spectroscopy, albedo) yield similar compositions.
TL;DR: In this paper, the spectral energy distributions (SEDs) of very young luminous extragalactic young stellar objects (YSOs) were analyzed using the HERITAGE science demonstration program.
Abstract: We demonstrate the unique capabilities of Herschel to study very young luminous extragalactic young stellar objects (YSOs) by analyzing a central strip of the Large Magellanic Cloud obtained through the HERITAGE science demonstration program. We combine PACS 100 and 160, and SPIRE 250, 350, and 500 μ m photometry with 2MASS (1.25-2.17 μ m) and Spitzer IRAC and MIPS (3.6-70 μ m) to construct complete spectral energy distributions (SEDs) of compact sources. From these, we identify 207 candidate embedded YSOs in the observed region, ~40% never-before identified. We discuss their position in far-infrared color-magnitude space, comparing with previously studied, spectroscopically confirmed YSOs and maser emission. All have red colors indicating massive cool envelopes and great youth. We analyze four example YSOs, determining their physical properties by fitting their SEDs with radiative transfer models. Fitting full SEDs including the Herschel data requires us to increase the size and mass of envelopes included in the models. This implies higher accretion rates (≳10-4 yr-1 ), in agreement with previous outflow studies of high-mass protostars. Our results show that Herschel provides reliable longwave SEDs of large samples of high-mass YSOs; discovers the youngest YSOs whose SEDs peak in Herschel bands; and constrains the physical properties and evolutionary stages of YSOs more precisely than was previously possible.
TL;DR: In this article, the authors determined the flux ratios of the heavy and eccentric planet XO-3b to its parent star in the four Infrared Array Camera bands of the Spitzer Space Telescope.
Abstract: We determined the flux ratios of the heavy and eccentric planet XO-3b to its parent star in the four Infrared Array Camera bands of the Spitzer Space Telescope: 0.101% +- 0.004% at 3.6 {mu}m; 0.143% +- 0.006% at 4.5 {mu}m; 0.134% +- 0.049% at 5.8 {mu}m; and 0.150% +- 0.036% at 8.0 {mu}m. The flux ratios are within [-2.2, 0.3, -0.8, and -1.7]sigma of the model of XO-3b with a thermally inverted stratosphere in the 3.6 {mu}m, 4.5 {mu}m, 5.8 {mu}m, and 8.0 {mu}m channels, respectively. XO-3b has a high illumination from its parent star (F{sub p} {approx} (1.9-4.2) x 10{sup 9} erg cm{sup -2} s{sup -1}) and is thus expected to have a thermal inversion, which we indeed observe. When combined with existing data for other planets, the correlation between the presence of an atmospheric temperature inversion and the substellar flux is insufficient to explain why some high insolation planets like TrES-3 do not have stratospheric inversions and some low insolation planets like XO-1b do have inversions. Secondary factors such as sulfur chemistry, atmospheric metallicity, amounts of macroscopic mixing in the stratosphere, or even dynamical weather effects likely play a role. Using the secondary eclipse timing centroids, we determinedmore » the orbital eccentricity of XO-3b as e = 0.277 +- 0.009. The model radius-age trajectories for XO-3b imply that at least some amount of tidal heating is required to inflate the radius of XO-3b, and the tidal heating parameter of the planet is constrained to Q{sub p} {approx}< 10{sup 6}.« less
TL;DR: In this paper, mid-IR and radio observations of the Galactic luminous blue variables (LBVs) candidate HD 168625 and its associated nebula were performed using the Infrared Spectrograph on board the Spitzer Space Telescope.
Abstract: We present mid-IR and radio observations of the Galactic luminous blue variables (LBVs) candidate HD 168625 and its associated nebula. We obtained mid-IR spectroscopic observations using the Infrared Spectrograph on board the Spitzer Space Telescope, and performed mid-IR and radio imaging observations using VISIR on the Very Large Telescope and the Very Large Array with comparable angular resolution. Our spectroscopic observations detected spectral features attributable to polycyclic aromatic hydrocarbons (PAHs) and therefore indicate the presence of a photodissociation region (PDR) around the ionized nebula. This result increases the number of LBVs and LBV candidates where a PDR has been found, confirming the importance of such a component in the total mass-loss budget of the central object during this elusive phase of massive star evolution. We have analyzed and compared the mid-IR and radio maps, and derive several results concerning the associated nebula. There is evidence for grain distribution variations across the nebula, with a predominant contribution from bigger grains in the northern part of the nebula while PAH and smaller grains are more concentrated in the southern part. A compact radio component located where there is a lack of thermal dust grains corroborates the presence of a shock in the southern nebula, which could arise as a consequence of the interaction of a fast outflow with the slower, expanding dusty nebula. Such a shock would be a viable means for PAH production as well as for changes in the grain size distribution. Finally, from the detection of a central radio component probably associated with the wind from the central massive supergiant, we derive a current mass-loss rate of ˙ �� )
TL;DR: In this article, the authors present observations of newly discovered 24 μm circumstellar structures detected with MIPS around three evolved stars in the Cygnus-X star-forming region.
Abstract: We present observations of newly discovered 24 μm circumstellar structures detected with MIPS around three evolved stars in the Cygnus-X star-forming region. One of the objects, BD+43 3710, has a bipolar nebula, possibly due to an outflow or a torus of material. A second, HBHA 4202-22, a Wolf-Rayet candidate, shows a circular shell of 24 μm emission suggestive of either a limb-brightened shell or disk seen face-on. No diffuse emission was detected around either of these two objects in the Spitzer 3.6-8 μm IRAC bands. The third object is the luminous blue variable candidate G79.29+0.46. We resolved the previously known inner ring in all four IRAC bands. The 24 μm emission from the inner ring extends ~1.'2 beyond the shorter wavelength emission, well beyond what can be attributed to the difference in resolutions between MIPS and IRAC. Additionally, we have discovered an outer ring of 24 μm emission, possibly due to an earlier episode of mass loss. For the two shell stars, we present the results of radiative transfer models, constraining the stellar and dust shell parameters. The shells are composed of amorphous carbon grains, plus polycyclic aromatic hydrocarbons in the case of G79.29+0.46. Both G79.29+0.46 and HBHA 4202-22 lie behind the main Cygnus-X cloud. Although G79.29+0.46 simply may be on the far side of the cloud, HBHA 4202-22 is unrelated to the Cygnus-X star formation region.
TL;DR: In this article, the authors identify 116 YSO candidates: 102 are well characterized by the YSO models, predominately Stage I, and 14 may be multiple sources or young sources with transition disks.
Abstract: We present analysis of the energetic star-forming region Henize 206 (N206) located near the southern edge of the Large Magellanic Cloud (LMC) based on photometric data from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE-LMC; IRAC 3.6, 4.5, 5.8, 8.0 μm and MIPS 24 μm), Infrared Survey Facility near-infrared survey (J, H, K s ), and the Magellanic Clouds Photometric Survey (MCPS UBVI) covering a wavelength range of 0.36-24 μm. Young stellar object (YSO) candidates are identified based upon their location in infrared color-magnitude space and classified by the shapes of their spectral energy distributions in comparison with a pre-computed grid of YSO models. We identify 116 YSO candidates: 102 are well characterized by the YSO models, predominately Stage I, and 14 may be multiple sources or young sources with transition disks. Careful examination of the individual sources and their surrounding environment allows us to identify a factor of ~14.5 more YSO candidates than have already been identified. The total mass of these well-fit YSO candidates is ~520 M ☉. We calculate a current star formation rate of 0.27 × 10–1 M ☉ yr–1 kpc–2. The distribution of YSO candidates appears to follow shells of neutral material in the interstellar medium.
TL;DR: In this article, the authors present an overview of the calibration and properties of data from the IRAC instrument aboard the Spitzer Space Telescope taken after the depletion of cryogen, and shortly afterward a two-month long calibration and characterization campaign was conducted.
Abstract: We present an overview of the calibration and properties of data from the IRAC instrument aboard the Spitzer Space Telescope taken after the depletion of cryogen. The cryogen depleted on 15 May 2009, and shortly afterward a two-month- long calibration and characterization campaign was conducted. The array temperature and bias setpoints were revised on 19 September 2009 to take advantage of lower than expected power dissipation by the instrument and to improve sensitivity. The final operating temperature of the arrays is 28.7 K, the applied bias across each detector is 500 mV and the equilibrium temperature of the instrument chamber is 27.55 K. The final sensitivities are essentially the same as the cryogenic mission with the 3.6 μm array being slightly less sensitive (10%) and the 4.5 μm array within 5% of the cryogenic sensitivity. The current absolute photometric uncertainties are 4% at 3.6 and 4.5 μm, and better than milli-mag photometry is achievable for long-stare photometric observations. With continued analysis, we expect the absolute calibration to improve to the cryogenic value of 3%. Warm IRAC operations fully support all science that was conducted in the cryogenic mission and all currently planned warm science projects (including Exploration Science programs). We expect that IRAC will continue to make ground-breaking discoveries in star formation, the nature of the early universe, and in our understanding of the properties of exoplanets.
TL;DR: In this article, high-resolution images of the Luminous Blue Variable IRAS 18576+0341 were obtained using the mid-infrared imager VISIR at the very large Telescope and the Very Large Array interferometer.
Abstract: High spatial and sensitivity images of the Luminous Blue Variable IRAS 18576+0341 were obtained using the mid-infrared imager VISIR at the Very Large Telescope and the Very Large Array interferometer. The resulting mid-infrared continuum maps show a similar clumpy and approximately circular symmetric nebula, which contrasts sharply with the asymmetry that characterizes the ionized component of the envelope, as evidenced from the radio and [Ne II] line images obtained with comparable spatial resolution. In particular, there is excellent overall agreement between the 12.8 μm map and the radio images, consistent with free-free emission from circumstellar ionized material surrounding a central stellar wind. The color temperature and optical depth maps obtained from mid-infrared images show only slight fluctuations, suggesting quite uniform dust characteristics over the dust shell. We explore various possibilities to understand the cause of the different morphology of the dusty and gaseous component of the circumstellar envelope which are compatible with the observations.
TL;DR: In this article, a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties.
Abstract: We present a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer, SAGE-SMC survey database, for which we present uniform photometry from 0.3-24 um in the UBVIJHKs+IRAC+MIPS24 bands. We compare the color magnitude diagrams and color-color diagrams to those of the Large Magellanic Cloud (LMC), finding that the brightest infrared sources in the SMC are also the red supergiants, supergiant B[e] (sgB[e]) stars, luminous blue variables, and Wolf-Rayet stars, with the latter exhibiting less infrared excess, the red supergiants being less dusty and the sgB[e] stars being on average less luminous. Among the objects detected at 24 um are a few very luminous hypergiants, 4 B-type stars with peculiar, flat spectral energy distributions, and all 3 known luminous blue variables. We detect a distinct Be star sequence, displaced to the red, and suggest a novel method of confirming Be star candidates photometrically. We find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared to the LMC, and that the SMC Be stars occur at higher luminosities. We estimate mass-loss rates for the red supergiants, confirming the correlation with luminosity even at the metallicity of the SMC. Finally, we confirm the new class of stars displaying composite A & F type spectra, the sgB[e] nature of 2dFS1804 and find the F0 supergiant 2dFS3528 to be a candidate luminous blue variable with cold dust.
TL;DR: In this paper, high-resolution images of the Luminous Blue Variable IRAS 18576+0341 were obtained using the mid-infrared imager VISIR at the very large Telescope and the Very Large Array interferometer.
Abstract: High spatial and sensitivity images of the Luminous Blue Variable IRAS 18576+0341 were obtained using the mid infrared imager VISIR at the Very Large Telescope and the Very Large Array interferometer. The resulting mid-infrared continuum maps show a similar clumpy and approximately circular symmetric nebula, which contrasts sharply with the asymmetry that characterizes the ionized component of the envelope, as evidenced from the radio and [Ne II] line images obtained with comparable spatial resolution. In particular, there is excellent overall agreement between the 12.8 micron map and the radio images, consistent with free-free emission from circumstellar ionized material surrounding a central stellar wind. The color temperature and optical depth maps obtained from mid-infrared images show only slight fluctuations, suggesting quite uniform dust characteristics over the dust shell. We explore various possibilities to understand the cause of the different morphology of the dusty and gaseous component of the circumstellar envelope which are compatible with the observations.
Journal Article•
TL;DR: In this article, the authors report on observations of near-Earth objects (NEOs) performed with IRAC as part of our on-going (2009-2011) Warm Spitzer NEO survey, the primary aim of which is to provide sizes and albedos of some 700 NEOs.
Abstract: We report on observations of near-Earth objects (NEOs) performed with IRAC as part of our on-going (2009-2011) Warm Spitzer NEO survey ("ExploreNEOs"), the primary aim of which is to provide sizes and albedos of some 700 NEOs. The emphasis of the work described here is an assessment of the overall accuracy of our survey results, which are based on a semi-empirical generalized model of asteroid thermal emission. The set of some 170 NEOs in our current Warm Spitzer results catalog contains 28 for which published taxonomic classifications are available, and 14 for which relatively reliable published diameters and albedos are available. From a comparison of the Warm Spitzer results with results expected on the basis of previous observations, we conclude that Warm Spitzer diameters and albedos are accurate to about 25% and 50%, respectively. Cases in which agreement with results from the literature is worse than expected are highlighted and discussed; these include the potential spacecraft target 138911 2001 AE2. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.
University of Manchester1, Iowa State University2, Hoffmann-La Roche3, Space Telescope Science Institute4, University of Missouri5, University of Virginia6, University of California, Berkeley7, University of Arizona8, Paris Diderot University9, Katholieke Universiteit Leuven10, California Institute of Technology11, Harvard University12, National Radio Astronomy Observatory13, Nagoya University14, University College London15, Imperial College London16, Keele University17, Max Planck Society18, Cornell University19, Institut d'Astrophysique de Paris20, Johns Hopkins University21, University of Toledo22, Space Science Institute23
TL;DR: The SAGE-Spec Spitzer Legacy program as mentioned in this paper is a spectroscopic follow-up to the SAGE LMC photometric survey of the Large Magellanic Cloud carried out with the Spitzer Space Telescope.
Abstract: The SAGE-Spec Spitzer Legacy program is a spectroscopic follow-up to the SAGE-LMC photometric survey of the Large Magellanic Cloud carried out with the Spitzer Space Telescope. We present an overview of SAGE-Spec and some of its first results. The SAGE-Spec program aims to study the life cycle of gas and dust in the Large Magellanic Cloud, and to provide information essential to the classification of the point sources observed in the earlier SAGE-LMC photometric survey. We acquired 224.6 hours of observations using the InfraRed Spectrograph and the SED mode of the Multiband Imaging Photometer for Spitzer. The SAGE-Spec data, along with archival Spitzer spectroscopy of objects in the Large Magellanic Cloud, are reduced and delivered to the community. We discuss the observing strategy, the specific data reduction pipelines applied and the dissemination of data products to the scientific community. Initial science results include the first detection of an extragalactic "21 um" feature towards an evolved star and elucidation of the nature of disks around RV Tauri stars in the Large Magellanic Cloud. Towards some young stars, ice features are observed in absorption. We also serendipitously observed a background quasar, at a redshift of z~0.14, which appears to be host-less.
TL;DR: In this article, the spectral energy distributions (SEDs) of very young luminous extragalactic young stellar objects (YSOs) were analyzed using the Herschel data.
Abstract: We demonstrate the unique capabilities of Herschel to study very young luminous extragalactic young stellar objects (YSOs) by analyzing a central strip of the Large Magellanic Cloud obtained through the HERITAGE Science Demonstration Program. We combine PACS 100 and 160, and SPIRE 250, 350, and 500 microns photometry with 2MASS (1.25-2.17 microns) and Spitzer IRAC and MIPS (3.6-70 microns) to construct complete spectral energy distributions (SEDs) of compact sources. From these, we identify 207 candidate embedded YSOs in the observed region, ~40% never-before identified. We discuss their position in far-infrared color-magnitude space, comparing with previously studied, spectroscopically confirmed YSOs and maser emission. All have red colors indicating massive cool envelopes and great youth. We analyze four example YSOs, determining their physical properties by fitting their SEDs with radiative transfer models. Fitting full SEDs including the Herschel data requires us to increase the size and mass of envelopes included in the models. This implies higher accretion rates (greater than or equal to 0.0001 M_sun/yr), in agreement with previous outflow studies of high-mass protostars. Our results show that Herschel provides reliable longwave SEDs of large samples of high-mass YSOs; discovers the youngest YSOs whose SEDs peak in Herschel bands; and constrains the physical properties and evolutionary stages of YSOs more precisely than was previously possible.
TL;DR: In this article, the authors present the photometric catalogs for the star-forming cluster NGC 602 in the wing of the Small Magellanic Cloud covering a range of wavelengths from optical HST/ACS (F555W, F814W) and SMARTS/ANDICAM (V, I) to infrared (Spitzer/IRAC 3.6, 4.5, 5.8, and 8 micron and MIPS 24 micron).
Abstract: We present the photometric catalogs for the star-forming cluster NGC 602 in the wing of the Small Magellanic Cloud covering a range of wavelengths from optical HST/ACS (F555W, F814W) and SMARTS/ANDICAM (V, I) to infrared (Spitzer/IRAC 3.6, 4.5, 5.8, and 8 micron and MIPS 24 micron). Combining this with IRSF (InfraRed Survey Facility) near-infrared photometry (J, H, Ks), we compare the young main sequence (MS) and pre-main sequence (PMS) populations prominent in the optical with the current young stellar object (YSO) populations revealed by the infrared (IR). We analyze the MS and PMS population with isochrones in color-magnitude diagrams to derive ages and masses. The optical data reveal ~565 PMS candidates, low mass Stage III YSOs. We characterize ~40 YSOs by fitting their spectral energy distributions (SEDs) to a grid of models (Robitaille et al. 2007) to derive luminosities, masses and evolutionary phase (Stage I-III). The higher resolution HST images reveal that ~70% of the YSO candidates are either multiples or protoclusters. For YSOs and PMS sources found in common, we find a consistency in the masses derived. We use the YSO mass function to derive a present-day star-formation rate of ~0.2-1.0 Msun/yr/kpc^2, similar to the rate derived from the optical star formation history suggesting a constant star formation rate for this region. We demonstrate a progression of star formation from the optical star cluster center to the edge of the star forming dust cloud. We derive lifetimes of a few 10^5 years for the YSO Stages I and II.
Journal Article•
TL;DR: In this paper, the bulk density of a binary asteroid, 1999DJ4, was derived based on Warm Spitzer observations and ground-based light curve data, and the density was found to be 1.6 g/cm3.
Abstract: The Warm Spitzer NEO survey, ExploreNEOs, will observe approximately 700 Near Earth Asteroids. Several of these objects are known to be binary asteroid systems. Binary systems are interesting due to the unique opportunity they present for determining the masses and densities of their constituent bodies. The calculations rely on a variety of data sources. The geometric albedo and effective diameter of the system are known via ExploreNEOs. Ground based light curve observations can give the orbital period and the secondary to primary diameter ratio of the system. In some cases, Arecibo radar observations provide the semi-major axis of the system. We report here the bulk density of one of these binaries in particular, asteroid 1999DJ4. The density derived is 1.6 g/cm3. For those cases where radar data is unavailable, we address the effectiveness and difficulties of using transit timing of a binary asteroid to determine the semi-major axis of the system . We discuss the viability of finding a bulk density based solely on Warm Spitzer observations and ground based light curve data.
Posted Content•
TL;DR: The ExploreNEOs project as mentioned in this paper uses the Spitzer Space Telescope in its Warm Spitzer mode to study the history of near Earth space by deriving the physical properties of a large number of NEVs.
Abstract: We have begun the ExploreNEOs project in which we observe some 700 Near Earth Objects (NEOs) at 36 and 45 microns with the Spitzer Space Telescope in its Warm Spitzer mode From these measurements and catalog optical photometry we derive albedos and diameters of the observed targets The overall goal of our ExploreNEOs program is to study the history of near-Earth space by deriving the physical properties of a large number of NEOs In this paper we describe both the scientific and technical construction of our ExploreNEOs program We present our observational, photometric, and thermal modeling techniques We present results from the first 101 targets observed in this program We find that the distribution of albedos in this first sample is quite broad, probably indicating a wide range of compositions within the NEO population Many objects smaller than one kilometer have high albedos (>035), but few objects larger than one kilometer have high albedos This result is consistent with the idea that these larger objects are collisionally older, and therefore possess surfaces that are more space weathered and therefore darker, or are not subject to other surface rejuvenating events as frequently as smaller NEOs
TL;DR: In this article, the authors determined the flux ratios of the heavy and eccentric planet XO-3b to its parent star in the four IRAC bands of the Spitzer Space Telescope.
Abstract: We determined the flux ratios of the heavy and eccentric planet XO-3b to its parent star in the four IRAC bands of the Spitzer Space Telescope: 0.101% +- 0.004% at 3.6 micron; 0.143% +- 0.006% at 4.5 micron; 0.134% +- 0.049% at 5.8 micron and 0.150% +- 0.036% at 8.0 micron. The flux ratios are within [-2.2,0.3, -0.8, -1.7]-sigma of the model of XO-3b with a thermally inverted stratosphere in the 3.6 micron, 4.5 micron, 5.8 micron and 8.0 micron channels, respectively. XO-3b has a high illumination from its parent star (Fp ~(1.9 - 4.2) x 10^9 ergs cm^-2 s^-1) and is thus expected to have a thermal inversion, which we indeed observe. When combined with existing data for other planets, the correlation between the presence of an atmospheric temperature inversion and the substellar flux is insufficient to explain why some high insolation planets like TrES-3 do not have stratospheric inversions and some low insolation planets like XO-1b do have inversions. Secondary factors such as sulfur chemistry, atmospheric metallicity, amounts of macroscopic mixing in the stratosphere or even dynamical weather effects likely play a role. Using the secondary eclipse timing centroids we determined the orbital eccentricity of XO-3b as e = 0.277 +- 0.009. The model radius-age trajectories for XO-3b imply that at least some amount of tidal-heating is required to inflate the radius of XO-3b, and the tidal heating parameter of the planet is constrained to Qp < 10^6 .