Search Publications
Relativistic X-Ray Lines from the Inner Accretion Disks Around Black Holes
Miller, J. M.
Relativistic X-ray emission lines from the inner accretion disks around black holes are reviewed. Recent observations with the Chandra X-ray Observatory, X-ray Multi-Mirror Mission-Newton, and Suzaku are revealing these lines to be good probes of strong gravitational effects. A number of important observational and theoretical developments are hig…
The Geneva-Copenhagen survey of the Solar neighbourhood II. New uvby calibrations and rediscussion of stellar ages, the G dwarf problem, age-metallicity diagram, and heating mechanisms of the disk
Holmberg, J.; Nordström, B.; Andersen, J.
Context: Ages, metallicities, space velocities, and Galactic orbits of stars in the Solar neighbourhood are fundamental observational constraints on models of galactic disk evolution. Understanding and minimising systematic errors and sample selection biases in the data is crucial for their interpretation.
Aims: We aim to consolidate the calib…
Chromospheric Anemone Jets as Evidence of Ubiquitous Reconnection
Matsumoto, Takuma; Shibata, Kazunari; Nishizuka, Naoto +19 more
The heating of the solar chromosphere and corona is a long-standing puzzle in solar physics. Hinode observations show the ubiquitous presence of chromospheric anemone jets outside sunspots in active regions. They are typically 3 to 7 arc seconds = 2000 to 5000 kilometers long and 0.2 to 0.4 arc second = 150 to 300 kilometers wide, and their veloci…
Weak Gravitational Lensing with COSMOS: Galaxy Selection and Shape Measurements
Koekemoer, Anton M.; Ellis, Richard S.; Leauthaud, Alexie +14 more
With a primary goal of conducting precision weak-lensing measurements from space, the COSMOS survey has imaged the largest contiguous area observed by Hubble Space Telescope to date, using the Advanced Camera for Surveys (ACS). This is the first paper in a series in which we describe our strategy for addressing the various technical challenges in …
The Shear Testing Programme 2: Factors affecting high-precision weak-lensing analyses
Refregier, Alexandre; Ellis, Richard; Schrabback, Tim +28 more
The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak-lensing measurement, in preparation for the next generation of wide-field surveys. We review 16 current and emerging shear-measurement methods in a common language, and assess their performance by running them (blindly) on simulated images…
The composition of Titan's stratosphere from Cassini/CIRS mid-infrared spectra
Bézard, Bruno; Vinatier, Sandrine; Lellouch, Emmanuel +22 more
We have analyzed data recorded by the Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft during the Titan flybys T0-T10 (July 2004-January 2006). The spectra characterize various regions on Titan from 70° S to 70° N with a variety of emission angles. We study the molecular signatures observed in the mid-infrared CIRS detector arr…
The X-Ray Properties of the Most Luminous Quasars from the Sloan Digital Sky Survey
Brandt, W. N.; Garmire, G. P.; Chartas, G. +4 more
Utilizing 21 new Chandra observations as well as archival Chandra, ROSAT, and XMM-Newton data, we study the X-ray properties of a representative sample of 59 of the most optically luminous quasars in the universe (Mi~-29.3 to -30.2) spanning a redshift range of z~1.5-4.5. Our full sample consists of 32 quasars from the Sloan Digital Sky…
Discovery of heavy negative ions in Titan's ionosphere
Lewis, G. R.; Coates, A. J.; Sittler, E. C. +3 more
Titan's ionosphere contains a rich positive ion population including organic molecules. Here, using CAPS electron spectrometer data from sixteen Titan encounters, we reveal the existence of negative ions. These ions, with densities up to ~100 cm-3, are in mass groups of 10-30, 30-50, 50-80, 80-110, 110-200 and 200+ amu/charge. During on…
Exciting dark matter and the INTEGRAL/SPI 511keV signal
Finkbeiner, Douglas P.; Weiner, Neal
We propose a dark matter candidate with an “excited state” 1 2 MeV above the ground state, which may be collisionally excited and deexcites by e+e- pair emission. By converting its kinetic energy into pairs, such a particle could produce a substantial fraction of the 511 keV line observed by the International Gamma-Ray Astrop…
Hubble Space Telescope Fine Guidance Sensor Parallaxes of Galactic Cepheid Variable Stars: Period-Luminosity Relations
Freedman, Wendy L.; Harrison, Thomas E.; Bean, Jacob L. +6 more
We present new absolute trigonometric parallaxes and relative proper motions for nine Galactic Cepheid variable stars: ell Car, ζ Gem, β Dor, W Sgr, X Sgr, Y Sgr, FF Aql, T Vul, and RT Aur. We obtain these results with astrometric data from Fine Guidance Sensor 1r, a white-light interferometer on the Hubble Space Telescope. We find absolute parall…