Search Publications
Investigation of Thickness and Electrical Resistivity of the Current Sheets in Solar Eruptions
Raymond, J. C.; Ko, Y. -K.; Lin, J. +1 more
A discussion of the thickness of current sheets in solar eruptions, d, led Lin et al. in 2007 to estimate very large values for the effective resistivity, η e . Here, we address some questions raised by that paper. We apply the limb synoptic map technique and find d between 5.0 × 104 and 4.6 × 105 km, increasing wi…
Giant cavities, cooling and metallicity substructure in Abell 2204
Fabian, A. C.; Sanders, J. S.; Taylor, G. B.
We present results from deep Chandra and XMM-Newton observations of the relaxed X-ray luminous galaxy cluster Abell 2204. We detect metallicity inhomogeneities in the intracluster medium on a variety of distance scales, from a ~12 kpc enhancement containing a few times 107 Msolar of iron in the centre to a region at 400 kpc r…
The Velocity Distribution of Nearby Stars from Hipparcos Data. I. The Significance of the Moving Groups
Bovy, Jo; Hogg, David W.; Roweis, Sam T.
We present a three-dimensional reconstruction of the velocity distribution of nearby stars (lsim100 pc) using a maximum likelihood density estimation technique applied to the two-dimensional tangential velocities of stars. The underlying distribution is modeled as a mixture of Gaussian components. The algorithm reconstructs the error-deconvolved d…
Amazonian-aged fluvial valley systems in a climatic microenvironment on Mars: Melting of ice deposits on the interior of Lyot Crater
Head, J. W.; Dickson, J. L.; Fassett, C. I.
Valley networks, regional drainage patterns suggesting liquid water stability at the surface, are confined to early in the history of Mars (the Noachian/Hesperian boundary and before), prior to a major climate transition to the hyperarid cold conditions of the Amazonian. Several later fluvial valley systems have been documented in specific Hesperi…
Recent Progress in Physics-Based Models of the Plasmasphere
André, Nicolas; Jordanova, Vania K.; Lemaire, Joseph F. +5 more
We describe recent progress in physics-based models of the plasmasphere using the fluid and the kinetic approaches. Global modeling of the dynamics and influence of the plasmasphere is presented. Results from global plasmasphere simulations are used to understand and quantify (i) the electric potential pattern and evolution during geomagnetic stor…
Suzaku Observation of a Hard Excess in 1H 0419 - 577: Detection of a Compton-Thick Partial-Covering Absorber
Turner, T. J.; Kraemer, S. B.; Reeves, J. N. +2 more
We present results from a 200 ks Suzaku observation of 1H 0419 - 577 taken during 2007 July. The source shows a strong excess of counts above 10 keV compared to the extrapolation of models based on previous data in the 0.5-10 keV band. The "hard excess" in 1H 0419 - 577 can be explained by the presence of a Compton-thick partial-covering absorber …
Hinode/Extreme-Ultraviolet Imaging Spectrometer Observations of the Temperature Structure of the Quiet Corona
Warren, Harry P.; Brooks, David H.; Watanabe, Tetsuya +1 more
We present a differential emission measure (DEM) analysis of the quiet solar corona on disk using data obtained by the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode. We show that the expected quiet-Sun DEM distribution can be recovered from judiciously selected lines, and that their average intensities can be reproduced to within 30%. W…
The Internal Structure of Coronal Mass Ejections: Are all Regular Magnetic Clouds Flux Ropes?
Poedts, S.; Lugaz, N.; Roussev, I. I. +1 more
In this Letter, we investigate the internal structure of a coronal mass ejection (CME) and its dynamics by invoking a realistic initiation mechanism in a quadrupolar magnetic setting. The study comprises a compressible three-dimensional magnetohydrodynamics simulation. We use an idealized model of the solar corona, into which we superimpose a quad…
Active Galactic Nuclei in Groups and Clusters of Galaxies: Detection and Host Morphology
Mulchaey, John S.; Martini, Paul; Jeltema, Tesla E. +2 more
The incidence and properties of active galactic nuclei (AGNs) in the field, groups, and clusters can provide new information about how these objects are triggered and fueled, similar to how these environments have been employed to study galaxy evolution. We have obtained new XMM-Newton observations of seven X-ray selected groups and poor clusters …
The geology of Hotei Regio, Titan: Correlation of Cassini VIMS and RADAR
Nicholson, Philip D.; Sotin, Christophe; Barnes, Jason W. +10 more
Joint Cassini VIMS and RADAR SAR data of ∼700-km-wide Hotei Regio reveal a rich collection of geological features that correlate between the two sets of images. The degree of correlation is greater than anywhere else seen on Titan. Central to Hotei Regio is a basin filled with cryovolcanic flows that are anomalously bright in VIMS data (in particu…