Showing papers by "Joseph L. Hora 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
Max Planck Society1, Charles University in Prague2, Seoul National University3, Korea Astronomy and Space Science Institute4, European Space Agency5, Planetary Science Institute6, Hungarian Academy of Sciences7, university of lille8, Centre national de la recherche scientifique9, University of Tennessee10, Japan Aerospace Exploration Agency11, Harvard University12, Carnegie Learning13, Johns Hopkins University Applied Physics Laboratory14, Northern Arizona University15, Japan Spaceguard Association16, Heidelberg University17
TL;DR: In this article, the authors combine radiometric and lightcurve inversion techniques in different ways to find the object's spin-axis orientation, its shape and to improve the quality of the key physical and thermal parameters.
Abstract: The JAXA Hayabusa-2 mission was approved in 2010 and launched on December 3, 2014. The spacecraft will arrive at the near-Earth asteroid 162173 Ryugu (1999 JU3 ) in 2018 where it will perform a survey, land and obtainsurface material, then depart in December 2019 and return to Earth in December 2020. We observed Ryugu with the Herschel Space Observatory in April 2012 at far-infrared thermal wavelengths, supported by several ground-based observations to obtain optical lightcurves. We reanalysed previously published Subaru-COMICS and AKARI-IRC observations and merged them with a Spitzer -IRS data set. In addition, we used a large set of Spitzer -IRAC observations obtained in the period January to May, 2013. The data set includes two complete rotational lightcurves and a series of ten “point-and-shoot” observations, all at 3.6 and 4.5 μ m. The almost spherical shape of the target together with the insufficient lightcurve quality forced us to combine radiometric and lightcurve inversion techniques in different ways to find the object’s spin-axis orientation, its shape and to improve the quality of the key physical and thermal parameters. Handling thermal data in inversion techniques remains challenging: thermal inertia, roughness or local structures influence the temperature distribution on the surface. The constraints for size, spin or thermal properties therefore heavily depend on the wavelengths of the observations. We find that the solution which best matches our data sets leads to this C class asteroid having a retrograde rotation with a spin-axis orientation of (λ = 310°−340°; β = −40° ± ~ 15°) in ecliptic coordinates, an effective diameter (of an equal-volume sphere) of 850 to 880 m, a geometric albedo of 0.044 to 0.050 and a thermal inertia in the range 150 to 300 J m-2 s-0.5 K-1 . Based on estimated thermal conductivities of the top-layer surface in the range 0.1 to 0.6 W K-1 m-1 , we calculated that the grain sizes are approximately equal to between 1 and 10 mm. The finely constrained values for this asteroid serve as a “design reference model”, which is currently used for various planning, operational and modelling purposes by the Hayabusa-2 team.
71 citations
TL;DR: It is argued that several sites of star formation are independent of one another in terms of their ages and physical conditions, based on the morphology of the clusters.
Abstract: We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color-magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions, even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions and, based on the morphology of the clusters, we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution-fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process, and then examined them to see if they are related to any massive star formation tracers such as UCH II regions, masers, or dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively, and found that groups of YSOs hosting MYSO candidates are positionally associated with H II regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.
28 citations
TL;DR: In this paper, the authors reported observations of color in the inner coma of Comet C/2013 UQ4 (Catalina) with the broadband B and R filters and found significant temporal variations of the color slope.
Abstract: We report observations of color in the inner coma of Comet C/2013 UQ4 (Catalina) with the broadband B and R filters. We find significant temporal variations of the color slope, ranging from -12.67 $\pm$ 8.16 \% per 0.1~$\mu$m up to $35.09 \pm 11.7$ \% per 0.1~$\mu$this http URL is significant that the comet changes color from red to blue over only a two-day period. Such dispersion cannot be characterized with an average color slope. We also observe Comet C/2013 UQ4 (Catalina) in infrared using Spitzer and find no significant CO/CO$_{2}$ gaseous species in its coma. Therefore, we classify Comet C/2013 UQ4 (Catalina) as a dust-rich comet and attribute the measured color slope to its dust. We analyze the color slope using the model of agglomerated debris particles and conclude that the C/2013 UQ4 coma was chemically heterogeneous, consisting of at least two components. The first component producing the bluest color is consistent with Mg-rich silicates. There are three different options for the second component producing the reddest color. This color is consistent with either Mg-Fe silicates, kerogen type II, or organic matter processed with a low dose of UV radiation.
28 citations
TL;DR: In this article, the authors used color-magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS nearinfrared data to determine the young stellar object (YSO) populations in W51 and W43.
Abstract: We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color-magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions and based on the morphology of the clusters we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution (SED)-fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process and then examined them to see if they are related to any massive star formation tracers such as UCH II regions, masers and dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively and found that groups of YSOs hosting MYSO candidates are positionally associated with H II regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.
19 citations
TL;DR: In this article, VRI spectrophotometry of 39 near-Earth asteroids (NEAs) observed with the Sutherland, South Africa, node of the Korea Microlensing Telescope Network (KMTNet) is presented.
Abstract: We present here VRI spectrophotometry of 39 near-Earth asteroids (NEAs) observed with the Sutherland, South Africa, node of the Korea Microlensing Telescope Network (KMTNet). Of the 39 NEAs, 19 were targeted, but because of KMTNet's large 2° × 2° field of view, 20 serendipitous NEAs were also captured in the observing fields. Targeted observations were performed within 44 days (median: 16 days, min: 4 days) of each NEA's discovery date. Our broadband spectrophotometry is reliable enough to distinguish among four asteroid taxonomies and we were able to confidently categorize 31 of the 39 observed targets as either an S-, C-, X-, or D-type asteroid by means of a Machine Learning algorithm approach. Our data suggest that the ratio between "stony" S-type NEAs and "not-stony" (C+X+D)-type NEAs, with H magnitudes between 15 and 25, is roughly 1:1. Additionally, we report ~1 hr light curve data for each NEA, and of the 39 targets, we were able to resolve the complete rotation period and amplitude for six targets and report lower limits for the remaining targets.
15 citations
01 Oct 2017
11 citations
Posted Content•
Harvard University1, University of Wisconsin–Whitewater2, California Institute of Technology3, University of California, Los Angeles4, Northern Arizona University5, University of Arizona6, Massachusetts Institute of Technology7, University of Chicago8, Pennsylvania State University9, University of Colorado Boulder10, McGill University11, University of Toledo12, University of Maryland, College Park13, University of California, Berkeley14, University of Tennessee15, American Museum of Natural History16, Carnegie Institution for Science17, Ohio State University18, University of Liège19, University of Western Ontario20, University of Groningen21
TL;DR: Yee et al. as mentioned in this paper made a strong science case for extending the current Warm Mission to December 2020, which can continue to make ground-breaking discoveries in those fields and provide crucial support to the NASA flagship missions JWST and WFIRST, as well as the upcoming TESS mission, and it will complement ground-based observations by LSST and the new large telescopes of the next decade.
Abstract: Author(s): Yee, Jennifer C; Fazio, Giovanni G; Benjamin, Robert; Kirkpatrick, J Davy; Malkan, Matt A; Trilling, David; Carey, Sean; Ciardi, David R; Apai, Daniel; Ashby, MLN; Ballard, Sarah; Bean, Jacob L; Beatty, Thomas; Berta-Thompson, Zach; Capak, P; Charbonneau, David; Chesley, Steven; Cowan, Nicolas B; Crossfield, Ian; Cushing, Michael C; Wit, Julien de; Deming, Drake; Dickinson, M; Dittmann, Jason; Dragomir, Diana; Dressing, Courtney; Emery, Joshua; Faherty, Jacqueline K; Gagne, Jonathan; Gaudi, B Scott; Gillon, Michael; Grillmair, Carl J; Harris, Alan; Hora, Joseph; Ingalls, James G; Kataria, Tiffany; Kreidberg, Laura; Krick, Jessica E; Lowrance, Patrick J; Mahoney, William A; Metchev, Stanimir A; Mommert, Michael; Mueller, Michael Migo; Shvartzvald, Yossi; Smith, Howard; Stevenson, Kevin B; Teplitz, HI; Willner, SP | Abstract: Although the final observations of the Spitzer Warm Mission are currently scheduled for March 2019, it can continue operations through the end of the decade with no loss of photometric precision. As we will show, there is a strong science case for extending the current Warm Mission to December 2020. Spitzer has already made major impacts in the fields of exoplanets (including microlensing events), characterizing near Earth objects, enhancing our knowledge of nearby stars and brown dwarfs, understanding the properties and structure of our Milky Way galaxy, and deep wide-field extragalactic surveys to study galaxy birth and evolution. By extending Spitzer through 2020, it can continue to make ground-breaking discoveries in those fields, and provide crucial support to the NASA flagship missions JWST and WFIRST, as well as the upcoming TESS mission, and it will complement ground-based observations by LSST and the new large telescopes of the next decade. This scientific program addresses NASA's Science Mission Directive's objectives in astrophysics, which include discovering how the universe works, exploring how it began and evolved, and searching for life on planets around other stars.
5 citations
TL;DR: In this article, VRI spectrophotometry of 39 near-Earth asteroids (NEAs) observed with the Sutherland, South Africa, node of the Korea Microlensing Telescope Network (KMTNet) is presented.
Abstract: We present here VRI spectrophotometry of 39 near-Earth asteroids (NEAs) observed with the Sutherland, South Africa, node of the Korea Microlensing Telescope Network (KMTNet). Of the 39 NEAs, 19 were targeted, but because of KMTNet's large 2 deg by 2 deg field of view, 20 serendipitous NEAs were also captured in the observing fields. Targeted observations were performed within 44 days (median: 16 days, min: 4 days) of each NEA's discovery date. Our broadband spectrophotometry is reliable enough to distinguish among four asteroid taxonomies and we were able to confidently categorize 31 of the 39 observed targets as either a S-, C-, X- or D-type asteroid by means of a Machine Learning (ML) algorithm approach. Our data suggest that the ratio between "stony" S-type NEAs and "not-stony" (C+X+D)-type NEAs, with H magnitudes between 15 and 25, is roughly 1:1. Additionally, we report ~1-hour light curve data for each NEA and of the 39 targets we were able to resolve the complete rotation period and amplitude for six targets and report lower limits for the remaining targets.
4 citations