Showing papers by "William T. Reach published in 2017"
University of Manchester1, Keele University2, Space Telescope Science Institute3, University College London4, Cornell University5, European Southern Observatory6, California Institute of Technology7, Air Force Research Laboratory8, Katholieke Universiteit Leuven9, Johns Hopkins University10, University of Virginia11, National Radio Astronomy Observatory12, Iowa State University13, Hoffmann-La Roche14, University of California, Berkeley15, Paris Diderot University16, University of Arizona17, Harvard University18, Nagoya University19, University of Missouri20, Imperial College London21, Max Planck Society22, University of Warsaw23, Institut d'Astrophysique de Paris24, University of Toledo25
TL;DR: In this article, a decision-tree method of object classification based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information was used to classify the SAGE-Spec sample of point sources.
Abstract: We present the classification of 197 point sources observed with the Infrared Spectrograph in the SAGE-Spec Legacy programme on the Spitzer Space Telescope. We introduce a decision-tree method of object classification based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information, which is used to classify the SAGE-Spec sample of point sources. The decision tree has a broad application to mid-infrared spectroscopic surveys, where supporting photometry and variability information are available. We use these classifications to make deductions about the stellar populations of the Large Magellanic Cloud and the success of photometric classification methods. We find 90 asymptotic giant branch (AGB) stars, 29 young stellar objects, 23 post-AGB objects, 19 red supergiants, eight stellar photospheres, seven background galaxies, seven planetary nebulae, two H_(II) regions and 12 other objects, seven of which remain unclassified.
128 citations
TL;DR: In this article, the authors present 5-35-µm thermal emission spectra of comets 10P/Tempel 2 and 49P/Arend-Rigaux observed with the Infrared Spectrograph on the Spitzer Space Telescope.
36 citations
TL;DR: In this paper, the authors identify a sample of isolated clouds, approximately 100 M ⊙ in size, and use the dust content to estimate the total amount of gas in the clouds.
Abstract: The content of interstellar clouds, in particular the inventory of diffuse molecular gas, remains uncertain. We identified a sample of isolated clouds, approximately 100 M ⊙ in size, and used the dust content to estimate the total amount of gas. In Paper I, the total inferred gas content was found significantly larger than that seen in 21 cm emission measurements of H i. In this paper we test the hypothesis that the apparent excess "dark" gas is cold H i, which would be evident in absorption but not in emission due to line saturation. The results show that there is not enough 21 cm absorption toward the clouds to explain the total amount of "dark" gas.
21 citations
TL;DR: In this paper, the FORCAST instrument on the Stratospheric Observatory for Infrared Astronomy (SOFIA) was used to map the zonal-mean temperature and para-H2 distribution in Jupiter's upper troposphere.
21 citations
TL;DR: In this paper, the authors study infrared emission of 17 isolated, diffuse clouds with masses of order to test the hypothesis that grain property variations cause the apparently low gas-to-dust ratios that have been measured in those clouds.
Abstract: We study infrared emission of 17 isolated, diffuse clouds with masses of order to test the hypothesis that grain property variations cause the apparently low gas-to-dust ratios that have been measured in those clouds. Maps of the clouds were constructed from Wide-field Infrared Survey Explorer (WISE) data and directly compared with the maps of dust optical depth from Planck. The mid-infrared emission per unit dust optical depth has a significant trend toward lower values at higher optical depths. The trend can be quantitatively explained by the extinction of starlight within the clouds. The relative amounts of polycyclic aromatic hydrocarbon and very small grains traced by WISE, compared with large grains tracked by Planck, are consistent with being constant. The temperature of the large grains significantly decreases for clouds with larger dust optical depth; this trend is partially due to dust property variations, but is primarily due to extinction of starlight. We updated the prediction for molecular hydrogen column density, taking into account variations in dust properties, and find it can explain the observed dust optical depth per unit gas column density. Thus, the low gas-to-dust ratios in the clouds are most likely due to "dark gas" that is molecular hydrogen.
17 citations
01 Oct 2017
1 citations