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  • Waters, Christopher  (18)
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  • 1
    Language: English
    In: The Astronomical Journal, 2012, Vol.143(6), p.142 (8pp)
    Description: We present the discovery of the first high-redshift ( z 〉 5.7) quasar from the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1 or PS1). This quasar was initially detected as an i P1 dropout in PS1, confirmed photometrically with the SAO Wide-field InfraRed Camera at Arizona's Multiple Mirror Telescope (MMT) and the Gamma-Ray Burst Optical/Near-Infrared Detector at the MPG 2.2 m telescope in La Silla. The quasar was verified spectroscopically with the MMT Spectrograph, Red Channel and the Cassegrain Twin Spectrograph at the Calar Alto 3.5 m telescope. Its near-infrared spectrum was taken at the Large Binocular Telescope Observatory (LBT) with the LBT Near-Infrared Spectroscopic Utility with Camera and Integral Field Unit for Extragalactic Research. It has a redshift of 5.73, an AB z P1 magnitude of 19.4, a luminosity of 3.8 × 10 47  erg s 1 , and a black hole mass of 6.9 × 10 9 M . It is a broad absorption line quasar with a prominent Ly peak and a very blue continuum spectrum. This quasar is the first result from the PS1 high-redshift quasar search that is projected to discover more than 100  i P1 dropout quasars and could potentially find more than 10 z P1 dropout ( z 〉 6.8) quasars.
    Keywords: Astrophysics, Cosmology And Astronomy ; Absorption ; Astronomy ; Astrophysics ; Black Holes ; Cameras ; Cosmic Gamma Bursts ; Infrared Spectra ; Luminosity ; Mirrors ; Near Infrared Radiation ; Quasars ; Red Shift ; Telescopes ; Universe ; Astronomy & Astrophysics;
    ISSN: 0004-6256
    E-ISSN: 1538-3881
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  • 2
    In: Monthly Notices of the Royal Astronomical Society, 2016, Vol. 457(1), pp.389-404
    Description: We present a systematic search for changing-look quasars based on repeat photometry from Sloan Digital Sky Survey (SDSS) and Pan-STARRS1, along with repeat spectra from SDSS and SDSS-III Baryon Oscillation Spectroscopic Survey. Objects with large, |Δ g | 〉 1 mag photometric variations in their light curves are selected as candidates to look for changes in broad emission line (BEL) features. Out of a sample of 1011 objects that satisfy our selection criteria and have more than one epoch of spectroscopy, we find 10 examples of quasars that have variable and/or ‘changing-look’ BEL features. Four of our objects have emerging BELs, five have disappearing BELs, and one object shows tentative evidence for having both emerging and disappearing BELs. With redshifts in the range 0.20 〈 z 〈 0.63, this sample includes the highest redshift changing-look quasars discovered to date. We highlight the quasar J102152.34+464515.6 at z = 0.204. Here, not only have the Balmer emission lines strongly diminished in prominence, including Hβ all but disappearing, but the blue continuum f ν ∝ν 1/3 typical of an active galactic nuclei is also significantly diminished in the second epoch of spectroscopy. Using our selection criteria, we estimate that 〉15 per cent of strongly variable luminous quasars display changing-look BEL features on rest-frame time-scales of 8 to 10 yr. Plausible time-scales for variable dust extinction are factors of 2–10 too long to explain the dimming and brightening in these sources, and simple dust reddening models cannot reproduce the BEL changes. On the other hand, an advancement such as disc reprocessing is needed if the observed variations are due to accretion rate changes.
    Keywords: Accretion, Accretion Discs ; Galaxies: Active ; Quasars: Emission Lines ; Quasars: General
    ISSN: 0035-8711
    E-ISSN: 1365-2966
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  • 3
    Language: English
    In: The Astrophysical Journal Letters, 2015, Vol.803(2), p.L16 (6pp)
    Description: Supermassive black hole binaries (SMBHBs) should be an inevitable consequence of the hierarchical growth of massive galaxies through mergers and the strongest sirens of gravitational waves (GWs) in the cosmos. Yet, their direct detection has remained elusive due to the compact (sub-parsec) orbital separations of gravitationally bound SMBHBs. Here, we exploit a theoretically predicted signature of an SMBHB in the time domain: periodic variability caused by a mass accretion rate that is modulated by the binary’s orbital motion. We report our first significant periodically varying quasar detection from the systematic search in the Pan-STARRS1 (PS1) Medium Deep Survey. Our SMBHB candidate, PSO J334.2028+01.4075, is a luminous radio-loud quasar at z = 2.060, with extended baseline photometry from the Catalina Real-Time Transient Survey, as well as archival spectroscopy from the FIRST Bright Quasar Survey. The observed period (542 ± 15 days) and estimated black hole mass ( ) correspond to an orbital separation of Schwarzschild radii ( pc), assuming the rest-frame period of the quasar variability traces the orbital period of the binary. This SMBHB candidate, discovered at the peak redshift for SMBH mergers, is in a physically stable configuration for a circumbinary accretion disk and within the regime of GW-driven orbital decay. Our search with PS1 is a benchmark study for the exciting capabilities of LSST, which will have orders of magnitude larger survey power and will potentially pinpoint the locations of thousands of SMBHBs in the variable night sky.
    Keywords: Binary Stars ; Gravity Waves ; Galaxies ; Black Holes ; Spectroscopy ; Quasars ; Stars, Universe (524) ; Quasars: General ; Surveys;
    ISSN: 2041-8205
    E-ISSN: 2041-8213
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  • 4
    In: Monthly Notices of the Royal Astronomical Society, 2018, Vol. 482(1), pp.715-731
    Description: A large sample of white dwarfs is selected by both proper motion and colours from the Pan-STARRS 1 $3\pi$ Steradian Survey Processing Version 2 to construct the white dwarf luminosity functions of the discs and halo in the solar neighbourhood. Four-parameter astrometric solutions were recomputed from the epoch data. The generalized maximum volume method is then used to calculate the density of the populations. After removal of crowded areas near the Galactic plane and centre, the final sky area used by this work is 7.833 sr, which is $83{{\ \rm per\ cent}}$ of the $3\pi$ sky and $62{{\ \rm per\ cent}}$ of the whole sky. By dividing the sky using Voronoi tessellation, photometric and astrometric uncertainties are recomputed at each step of the integration to improve the accuracy of the maximum volume. Interstellar reddening is considered throughout the work. We find a disc-to-halo white dwarf ratio of about 100.
    Keywords: Surveys ; Proper Motions ; Stars: Luminosity Function, Mass Function ; White Dwarfs ; Solar Neighbourhood
    ISSN: 0035-8711
    E-ISSN: 1365-2966
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  • 5
    In: Monthly Notices of the Royal Astronomical Society, 2018, Vol. 478(1), pp.651-666
    Description: We present a new 3D map of interstellar dust reddening, covering three quarters of the sky (declinations of δ ≳ −30°) out to a distance of several kiloparsecs. The map is based on high-quality stellar photometry of 800 million stars from Pan-STARRS 1 and 2MASS. We divide the sky into sightlines containing a few hundred stars each, and then infer stellar distances and types, along with the line-of-sight dust distribution. Our new map incorporates a more accurate average extinction law and an additional 1.5 yr of Pan-STARRS 1 data, tracing dust to greater extinctions and at higher angular resolutions than our previous map. Out of the plane of the Galaxy, our map agrees well with 2D reddening maps derived from far-infrared dust emission. After accounting for a 25 per cent difference in scale, we find a mean scatter of ∼10 per cent between our map and the Planck far-infrared emission-based dust map, out to a depth of 0.8 mag in E ( g P1  −  r P1 ), with the level of agreement varying over the sky. Our map can be downloaded at http://argonaut.skymaps.info , or from the Harvard Dataverse (Green 2017 ).
    Keywords: Dust, Extinction ; Ism: Structure ; Galaxy: Structure
    ISSN: 0035-8711
    E-ISSN: 1365-2966
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  • 6
    Language: English
    In: The Astrophysical Journal, 2016, Vol.821(2), p.120 (31pp)
    Description: Substellar members of young (≲150 Myr) moving groups are valuable benchmarks to empirically define brown dwarf evolution with age and to study the low-mass end of the initial mass function. We have combined Pan-STARRS1 (PS1) proper motions with optical–IR photometry from PS1, Two Micron All Sky Survey (2MASS), and WISE to search for substellar members of the AB Dor Moving Group within ≈50 pc and with spectral types of late M to early L, corresponding to masses down to ≈30 M Jup at the age of the group (≈125 Myr). Including both photometry and proper motions allows us to better select candidates by excluding field dwarfs whose colors are similar to young AB Dor Moving Group members. Our near-IR spectroscopy has identified six ultracool dwarfs (M6–L4; ≈30–100 M Jup ) with intermediate surface gravities ( int-g ) as candidate members of the AB Dor Moving Group. We find another two candidate members with spectra showing hints of youth but consistent with field gravities. We also find four field brown dwarfs unassociated with the AB Dor Moving Group, three of which have int-g gravity classification. While signatures of youth are present in the spectra of our ≈125 Myr objects, neither their J – K nor W 1 – W 2 colors are significantly redder than field dwarfs with the same spectral types, unlike younger ultracool dwarfs. We also determined PS1 parallaxes for eight of our candidates and one previously identified AB Dor Moving Group candidate. Although radial velocities (and parallaxes, for some) are still needed to fully assess membership, these new objects provide valuable insight into the spectral characteristics and evolution of young brown dwarfs.
    ISSN: 0004-637X
    E-ISSN: 1538-4357
    Source: IOPscience (IOP Publishing)
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  • 7
    Language: English
    In: The Astrophysical Journal, 2018, Vol.854(2), p.79 (20pp)
    Description: We present a simple but effective technique for measuring angular variation in R V across the sky. We divide stars from the Pan-STARRS1 catalog into Healpix pixels and determine the posterior distribution of reddening and R V for each pixel using two independent Monte Carlo methods. We find the two methods to be self-consistent in the limits where they are expected to perform similarly. We also find some agreement with high-precision photometric studies of R V in Perseus and Ophiuchus, as well as with a map of reddening near the Galactic plane based on stellar spectra from APOGEE. While current studies of R V are mostly limited to isolated clouds, we have developed a systematic method for comparing R V values for the majority of observable dust. This is a proof of concept for a more rigorous Galactic reddening map.
    Keywords: Astronomy & Astrophysics ; Physics;
    ISSN: 0004-637X
    E-ISSN: 1538-4357
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  • 8
    Language: English
    In: Quick submit: 2017-05-16T17:52:02-0400
    Description: We present the discovery of a new dwarf galaxy, Perseus I/Andromeda XXXIII, found in the vicinity of Andromeda (M31) in stacked imaging data from the Pan-STARRS1 3π survey. Located 27fdg9 away from M31, Perseus I has a heliocentric distance of 785 ± 65 kpc, compatible with it being a satellite of M31 at $374^{+14}_{-10}{\rm \,kpc}$ from its host. The properties of Perseus I are typical for a reasonably bright dwarf galaxy (MV = –10.3 ± 0.7), with an exponential half-light radius of rh = 1.7 ± 0.4 arcmin or $r_h = 400^{+105}_{-85}{\rm \,pc}$ at this distance, and a moderate ellipticity ($\epsilon = 0.43^{+0.15}_{-0.17}$). The late discovery of Perseus I is due to its fairly low surface brightness ($\mu _0=25.7^{+1.0}_{-0.9}$ mag arcsec–2), and to the previous lack of deep, high quality photometric data in this region. If confirmed to be a companion of M31, the location of Perseus I, far east from its host, could place interesting constraints on the bulk motion of the satellite system of M31.
    Keywords: Galaxies: Individual (Perseus I, Andromeda Xxxiii) ; Local Group
    ISSN: Martin, Nicolas F., Edward F. Schlafly, Colin T. Slater, Edouard J. Bernard, Hans-Walter Rix, Eric F. Bell, Annette M. N. Ferguson, et al. 2013. “Perseus I: A Distant Satellite Dwarf Galaxy of Andromeda.” The Astrophysical Journal 779 (1) (November 26): L10. doi:10.1088/2041-8205/779/1/l10.
    ISSN: 2041-8205
    E-ISSN: 20418213
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  • 9
    Language: English
    In: Icarus, 01 March 2015, Vol.248, pp.289-312
    Description: We analyze a set of 760 475 observations of 333 026 unique main-belt objects obtained by the Pan-STARRS1 (PS1) survey telescope between 2012 May 20 and 2013 November 9, a period during which PS1 discovered two main-belt comets, P/2012 T1 (PANSTARRS) and P/2013 R3 (Catalina-PANSTARRS). PS1 comet detection procedures currently consist of the comparison of the point spread functions (PSFs) of moving objects to those of reference stars, and the flagging of objects that show anomalously large radial PSF widths for human evaluation and possible observational follow-up. Based on the number of missed discovery opportunities among comets discovered by other observers, we estimate an upper limit comet discovery efficiency rate of ∼70% for PS1. Additional analyses that could improve comet discovery yields in future surveys include linear PSF analysis, modeling of trailed stellar PSFs for comparison to trailed moving object PSFs, searches for azimuthally localized activity, comparison of point-source-optimized photometry to extended-source-optimized photometry, searches for photometric excesses in objects with known absolute magnitudes, and crowd-sourcing. Analysis of the discovery statistics of the PS1 survey indicates an expected fraction of 59 MBCs per outer main-belt asteroids (corresponding to a total expected population of ∼140 MBCs among the outer main-belt asteroid population with absolute magnitudes of ), and a 95% confidence upper limit of 96 MBCs per outer main-belt asteroids (corresponding to a total of ∼230 MBCs), assuming a detection efficiency of 50%. We note however that significantly more sensitive future surveys (particularly those utilizing larger aperture telescopes) could detect many more MBCs than estimated here. Examination of the orbital element distribution of all known MBCs reveals an excess of high eccentricities ( ) relative to the background asteroid population. Theoretical calculations show that, given these eccentricities, the sublimation rate for a typical MBC is orders of magnitude larger at perihelion than at aphelion, providing a plausible physical explanation for the observed behavior of MBCs peaking in observed activity strength near perihelion. These results indicate that the overall rate of mantle growth should be slow, consistent with observational evidence that MBC activity can be sustained over multiple orbit passages.
    Keywords: Asteroids ; Comets ; Astrobiology ; Asteroids, Composition ; Comets, Origin ; Astronomy & Astrophysics
    ISSN: 0019-1035
    E-ISSN: 1090-2643
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  • 10
    In: Monthly Notices of the Royal Astronomical Society, 2014, Vol. 442(4), pp.2999-3009
    Description: We present the fiducial sequences of a sample of Galactic star clusters in the five bands of the Pan-STARRS1 (PS1) photometric system ( g P1 , r P1 , i P1 , z P1 , and y P1 ). These empirical sequences – which include the red giant and sub-giant branches, the main sequence, and the horizontal branch – were defined from deep colour–magnitude diagrams reaching below the oldest main-sequence turn-offs of 13 globular and 3 old open clusters covering a wide range of metallicities ( − 2.4 ≲ [Fe/H] ≲ +0.4). We find excellent agreement for the nine clusters in common with previous studies in similar photometric systems when transformed to the PS1 system. Because the photometric and spectroscopic properties of these stellar populations are accurately known, the fiducials provide a solid basis for the interpretation of observations in the PS1 system, as well as valuable constraints to improve the empirical colour– T eff relations.
    Keywords: Surveys ; Stars: Evolution ; Hertzsprung–Russell And Colour–Magnitude Diagrams ; Globular Clusters: General ; Open Clusters And Associations: General
    ISSN: 0035-8711
    E-ISSN: 1365-2966
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