Search Publications
Dayside and nightside magnetic field responses at 780 km altitude to dayside reconnection
Snekvik, K.; Østgaard, N.; Tenfjord, P. +4 more
During southward interplanetary magnetic field, dayside reconnection will drive the Dungey cycle in the magnetosphere, which is manifested as a two-cell convection pattern in the ionosphere. We address the response of the ionospheric convection to changes in the dayside reconnection rate by examining magnetic field perturbations at 780 km altitude…
A Comparison of Two Methods for Estimating Black Hole Spin in Active Galactic Nuclei
Haggard, Daryl; Capellupo, Daniel M.; Wafflard-Fernandez, Gaylor
Angular momentum, or spin, is a fundamental property of black holes (BHs), yet it is much more difficult to estimate than mass or accretion rate (for actively accreting systems). In recent years, high-quality X-ray observations have allowed for detailed measurements of the Fe Kα emission line, where relativistic line broadening allows constraints …
Temperature and density structure of a recurring active region jet
Del Zanna, Giulio; Mulay, Sargam M.; Mason, Helen
Aims: We present a study of a recurring jet observed on October 31, 2011 by the Atmosphereic Imaging Assembly (AIA) on board the Solar Dynamic Observatory, the X-ray Telescope (XRT) and EUV Imaging Spectrometer (EIS) on board Hinode. We discuss the physical parameters of the jet that are obtained using imaging and spectroscopic observations, …
The parameterization of wave-particle interactions in the Outer Radiation Belt
Forsyth, C.; Rae, I. J.; Murphy, K. R. +3 more
We explore the use of mean value empirical wave models in diffusion models of the Outer Radiation Belt. We show that magnetospheric wave power is not normally distributed in time and that geomagnetic activity does not provide a deterministic proxy for the temporal variability of wave activity. Our findings indicate that current diffusion models si…
IUVS echelle-mode observations of interplanetary hydrogen: Standard for calibration and reference for cavity variations between Earth and Mars during MAVEN cruise
Bertaux, Jean-Loup; Chaufray, Jean-Yves; Stewart, Ian +11 more
The high-resolution echelle mode of the Imaging Ultraviolet Spectrograph (IUVS) instrument on the Mars Atmosphere and Volatile Evolution mission has been designed to measure D and H Lyman α emissions from the Martian atmosphere to obtain key information about the physical processes by which water escapes into space. Toward this goal, the absolute …
Far-UV spectroscopy of two extremely hot, helium-rich white dwarfs
Rauch, T.; Werner, K.; Kruk, J. W.
A large proportion of hot post-asymptotic giant branch stars and white dwarfs (WDs) are hydrogen-deficient. Two distinct evolutionary sequences have been identified. One of them comprises stars of spectral type [WC] and PG1159, and it originates from a late helium-shell flash, creating helium-rich stellar atmospheres with significant admixtures of…
Does the radial-tangential macroturbulence model adequately describe the spectral line broadening of solar-type stars?*
Takeda, Yoichi; UeNo, Satoru
In incorporating the effect of atmospheric turbulence in the broadening of spectral lines, the so-called radial-tangential macroturbulence (RTM) model has been widely used in the field of solar-type stars, which was devised from intuitive appearance of the granular velocity field of the Sun. Since this model assumes that turbulent motions are rest…
Constraining the Physical State of the Hot Gas Halos in NGC 4649 and NGC 5846
Trinchieri, Ginevra; Romanowsky, Aaron J.; Brodie, Jean +15 more
We present results of a joint Chandra/XMM-Newton analysis of the early-type galaxies NGC 4649 and NGC 5846 aimed at investigating differences between mass profiles derived from X-ray data and those from optical data, to probe the state of the hot interstellar medium (ISM) in these galaxies. If the hot ISM is at a given radius in hydrostatic equili…
The X-Ray Reflection Spectrum of the Radio-loud Quasar 4C 74.26
Harrison, F. A.; Zhang, W. W.; Fabian, Andrew C. +11 more
The relativistic jets created by some active galactic nuclei are important agents of AGN feedback. In spite of this, our understanding of what produces these jets is still incomplete. X-ray observations, which can probe the processes operating in the central regions in the immediate vicinity of the supermassive black hole, the presumed jet launchi…
Fusion of photogrammetric and photoclinometric information for high-resolution DEMs from Mars in-orbit imagery
Luo, Bin; Douté, Sylvain; Jiang, Cheng +1 more
High-resolution Digital Elevation Models (DEMs) of the Martian surface are instrumental for studying the red planet. The Mars Orbiter Laser Altimeter (MOLA) instrument onboard the Mars Global Surveyor provided global DEM of high vertical resolution but with a limited spatial resolution that is not enough for characterizing small geological objects…