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  • Hodapp, Klaus  (28)
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  • 1
    Language: English
    In: The Astrophysical Journal, 2013, Vol.773(1), p.63 (15pp)
    Description: We have combined optical and NIR photometry from Pan-STARRS 1 and UKIDSS to search the young (5-10 Myr) star-forming region of Upper Scorpius for wide (400-4000 AU) substellar companions down to 5 M Jup . Our search is 4 mag deeper than previous work based on the Two Micron All Sky Survey. We identified several candidates around known stellar members using a combination of color selection and spectral energy distribution fitting. Our follow-up spectroscopy has identified two new companions as well as confirmed two companions previously identified from photometry, with spectral types of M7.5-M9 and masses of 15-60 M Jup , indicating a frequency for such wide substellar companions of 0.6% ± 0.3%. Both USco 16101913B and USco 16121800B are more luminous than expected for their spectral type compared with known members of Upper Sco. HIP 77900B has an extreme mass ratio ( M 2 / M 1 0.005) and an extreme separation of 3200 AU. USco 16022401B also has a very large separation of 1000 AU. We have also confirmed a low-mass stellar companion, USco 16102502B (730 AU, M5.5). Our substellar companions appear both non-coeval with their primary stars according to evolutionary models and, as a group, are systematically more luminous than the Upper Sco cluster sequence. One possible reason for these luminosity discrepancies could be different formation processes or accretion histories for these objects.
    Keywords: Astrophysics, Cosmology And Astronomy ; Color ; Energy Spectra ; Luminosity ; Mass ; Near Infrared Radiation ; Photometry ; Sky ; Spectroscopy ; Stars;
    ISSN: 0004-637X
    E-ISSN: 1538-4357
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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    Language: English
    In: The Astrophysical Journal, 2018, Vol.859(1), p.31 (32pp)
    Description: We characterize the spatial density of the Pan-STARRS1 (PS1) sample of Rrab stars to study the properties of the old Galactic stellar halo. This sample, containing 44,403 sources, spans galactocentric radii of 0.55 kpc ≤  R gc  ≤ 141 kpc with a distance precision of 3% and thus is able to trace the halo out to larger distances than most previous studies. After excising stars that are attributed to dense regions such as stellar streams, the Galactic disk and bulge, and halo globular clusters, the sample contains ∼11,000 sources within 20 kpc ≤  R gc  ≤ 131 kpc. We then apply forward modeling using Galactic halo profile models with a sample selection function. Specifically, we use ellipsoidal stellar density models ρ ( l , b , R gc ) with a constant and a radius-dependent halo flattening q ( R gc ). Assuming constant flattening q , the distribution of the sources is reasonably well fit by a single power law with and and comparably well fit by an Einasto profile with , an effective radius r eff  = 1.07 ± 0.10 kpc, and a halo flattening of q  = 0.923 ± 0.007. If we allow for a radius-dependent flattening q ( R gc ), we find evidence for a distinct flattening of q  ∼ 0.8 of the inner halo at ∼25 kpc. Additionally, we find that the south Galactic hemisphere is more flattened than the north Galactic hemisphere. The results of our work are largely consistent with many earlier results (e.g., Watkins et al.; Iorio et al.). We find that the stellar halo, as traced in RR Lyrae stars, exhibits a substantial number of further significant over- and underdensities, even after masking all known overdensities.
    Keywords: Astrophysics - Astrophysics Of Galaxies;
    ISSN: 0004-637X
    E-ISSN: 1538-4357
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  • 9
    Language: English
    In: The Astrophysical Journal, 2015, Vol.810(1), p.25 (23pp)
    Description: We present a three-dimensional map of interstellar dust reddening, covering three-quarters of the sky out to a distance of several kiloparsecs, based on Pan-STARRS 1 (PS1) and 2MASS photometry. The map reveals a wealth of detailed structure, from filaments to large cloud complexes. The map has a hybrid angular resolution, with most of the map at an angular resolution of – , and a maximum distance resolution of . The three-dimensional distribution of dust is determined in a fully probabilistic framework, yielding the uncertainty in the reddening distribution along each line of sight, as well as stellar distances, reddenings, and classifications for 800 million stars detected by PS1. We demonstrate the consistency of our reddening estimates with those of two-dimensional emission-based maps of dust reddening. In particular, we find agreement with the Planck -based reddening map to within in to a depth of , and explore systematics at reddenings less than . We validate our per-star reddening estimates by comparison with reddening estimates for stars with both Sloan Digital Sky Survey photometry and Sloan Extension for Galactic Understanding and Exploration spectral classifications, finding per-star agreement to within out to a stellar of 1 mag. We compare our map to two existing three-dimensional dust maps, by Marshall et al. and Lallement et al., demonstrating our finer angular resolution, and better distance resolution compared to the former within . The map can be queried or downloaded at http://argonaut.skymaps.info . We expect the three-dimensional reddening map presented here to find a wide range of uses, among them correcting for reddening and extinction for objects embedded in the plane of the Galaxy, studies of Galactic structure, calibration of future emission-based dust maps, and determining distances to objects of known reddening.
    Keywords: Astrophysics - Astrophysics Of Galaxies;
    ISSN: 0004-637X
    E-ISSN: 1538-4357
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  • 10
    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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