Search Publications
X-Ray and Multiwavelength Insights into the Nature of Weak Emission-line Quasars at Low Redshift
Brandt, W. N.; Hall, Patrick B.; Anderson, Scott F. +5 more
We report on the X-ray and multiwavelength properties of 11 radio-quiet quasars with weak or no emission lines identified by the Sloan Digital Sky Survey (SDSS) with redshift z = 0.4-2.5. Our sample was selected from the Plotkin et al. catalog of radio-quiet, weak-featured active galactic nuclei (AGNs). The distribution of relative X-ray brightnes…
Isotopic Ratios in Titan's Methane: Measurements and Modeling
Irwin, P. G. J.; Teanby, N. A.; Flasar, F. M. +10 more
The existence of methane in Titan's atmosphere (~6% level at the surface) presents a unique enigma, as photochemical models predict that the current inventory will be entirely depleted by photochemistry in a timescale of ~20 Myr. In this paper, we examine the clues available from isotopic ratios (12C/13C and D/H) in Titan's m…
The Spectrum of the Recycled PSR J0437-4715 and Its White Dwarf Companion
Pavlov, George G.; Kargaltsev, Oleg; Kaplan, David L. +4 more
We present extensive spectral and photometric observations of the recycled pulsar/white dwarf binary containing PSR J0437-4715, which we analyzed together with archival X-ray and gamma-ray data, to obtain the complete mid-infrared to gamma-ray spectrum. We first fit each part of the spectrum separately, and then the whole multi-wavelength spectrum…
The Magnetic Energy-Helicity Diagram of Solar Active Regions
Georgoulis, Manolis K.; Tziotziou, Kostas; Raouafi, Nour-Eddine
Using a recently proposed nonlinear force-free method designed for single-vector magnetograms of solar active regions, we calculate the instantaneous free magnetic energy and relative magnetic helicity budgets in 162 vector magnetograms corresponding to 42 different active regions. We find a statistically robust, monotonic correlation between the …
Time-resolved Ultraviolet Spectroscopy of the M-dwarf GJ 876 Exoplanetary System
Roberge, Aki; France, Kevin; Linsky, Jeffrey L. +2 more
Extrasolar planets orbiting M-stars may represent our best chance to discover habitable worlds in the coming decade. The ultraviolet spectrum incident upon both Earth-like and Jovian planets is critically important for proper modeling of their atmospheric heating and chemistry. In order to provide more realistic inputs for atmospheric models of pl…
Gas Emissions in Planck Cold Dust Clumps—A Survey of the J = 1-0 Transitions of 12CO, 13CO, and C18O
Li, Di; Liu, Tie; Qin, Sheng-Li +3 more
A survey toward 674 Planck cold clumps of the Early Cold Core Catalogue (ECC) in the J = 1-0 transitions of 12CO, 13CO, and C18O has been carried out using the Purple Mountain Observatory 13.7 m telescope. Six hundred seventy-three clumps were detected with 12CO and 13CO emission, and 68% of t…
Non-neutralized Electric Current Patterns in Solar Active Regions: Origin of the Shear-generating Lorentz Force
Mikić, Zoran; Georgoulis, Manolis K.; Titov, Viacheslav S.
Using solar vector magnetograms of the highest available spatial resolution and signal-to-noise ratio, we perform a detailed study of electric current patterns in two solar active regions (ARs): a flaring/eruptive and a flare-quiet one. We aim to determine whether ARs inject non-neutralized (net) electric currents in the solar atmosphere, respondi…
Distance and Kinematics of the Red Hypergiant VY CMa: Very Long Baseline Array and Very Large Array Astrometry
Menten, K. M.; Zhang, B.; Reid, M. J. +1 more
We report astrometric results of phase-referencing very long baseline interferometry observations of 43 GHz SiO maser emission toward the red hypergiant VY Canis Majoris (VY CMa) using the Very Long Baseline Array (VLBA). We measured a trigonometric parallax of 0.83 ± 0.08 mas, corresponding to a distance of 1.20+0.13 -0.10 k…
Photoevaporating Proplyd-like Objects in Cygnus OB2
Drake, Jeremy J.; Gutermuth, Robert A.; Wright, Nicholas J. +4 more
We report the discovery of 10 proplyd-like objects in the vicinity of the massive OB association Cygnus OB2. They were discovered in IPHAS Hα images and are clearly resolved in broadband Hubble Space Telescope/Advanced Camera for Surveys, near-IR, and Spitzer mid-IR images. All exhibit the familiar tadpole shape seen in photoevaporating objects su…
A Detection of Weak-lensing Magnification Using Galaxy Sizes and Magnitudes
Koekemoer, Anton M.; Leauthaud, Alexie; Massey, Richard +5 more
Weak lensing is commonly measured using shear through galaxy ellipticities or using the effect of magnification bias on galaxy number densities. Here, we report on the first detection of weak-lensing magnification with a new, independent technique using the distribution of galaxy sizes and magnitudes. These data come for free in galaxy surveys des…