Search Publications
FeXXV and FeXXVI lines from low-velocity, photoionized gas in the X-ray spectra of active galactic nuclei
Nicastro, Fabrizio; Bianchi, Stefano; Matt, Giorgio +2 more
We have calculated the equivalent widths of the absorption lines produced by FeXXV and FeXXVI in a Compton-thin, low-velocity photoionized material illuminated by the nuclear continuum in active galactic nuclei. The results, plotted against the ionization parameter and the column density of the gas, are a complement to those presented by Bianchi &…
Saturn's vertical and latitudinal cloud structure 1991 2004 from HST imaging in 30 filters
Karkoschka, Erich; Tomasko, Martin
We analyzed 134 images of Saturn taken by the Hubble Space Telescope between 1991 and 2004. The images cover wavelengths between 231 and 2370 nm in 30 filters. We combined some 10 million calibrated reflectivity measurements into 18,000 center-to-limb curves. We used the method of principal component analysis to find the main latitudinal and tempo…
A Remarkable Low-Mass X-Ray Binary within 0.1 Parsecs of the Galactic Center
Brandt, W. N.; Ghez, A. M.; Muno, M. P. +5 more
Recent X-ray and radio observations by Muno et al. and Bower et al. have identified a transient low-mass X-ray binary (LMXB) located only 0.1 pc in projection from the Galactic center, CXOGC J174540.0-290031. In this paper, we report the detailed analysis of X-ray and infrared observations of the transient and its surroundings. Chandra observation…
Optimal reconstruction of magnetopause structures from Cluster data
Klecker, B.; Hasegawa, H.; Dunlop, M. W. +3 more
The Grad-Shafranov (GS) reconstruction technique, a single-spacecraft based data analysis method for recovering approximately two-dimensional (2-D) magnetohydrostatic plasma/field structures in space, is improved to become a multi-spacecraft technique that produces a single field map by ingesting data from all four Cluster spacecraft into the calc…
X-ray quasi-periodic pulsations in solar flares as magnetohydrodynamic oscillations
Fletcher, L.; Foullon, C.; Nakariakov, V. M. +1 more
We report the first observation at high spatial resolution of long-period quasi-periodic pulsations (QPP) of X-ray radiation during solar flares, made possible with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), supported by complementary data at other wavelengths from space-based and ground-based telescopes. Evidence for the p…
Radial evolution of cross helicity in high-latitude solar wind
Bavassano, B.; Matthaeus, W. H.; Bieber, J. W. +4 more
We employ a turbulence transport theory to explain the high-latitude radial evolution of cross helicity, or Alfvénicity, observed by the Ulysses spacecraft. Evolution is slower than at low latitudes due to weakened shear driving.
An Analysis of the Shapes of Ultraviolet Extinction Curves. IV. Extinction without Standards
Fitzpatrick, E. L.; Massa, D.
In this paper we present a new method for deriving UV through IR extinction curves, based on the use of stellar atmosphere models to provide estimates of the intrinsic (i.e., unreddened) stellar spectral energy distributions (SEDs), rather than unreddened (or lightly reddened) standard stars. We show that this ``extinction without standards'' tech…
Characteristics of the magnetosheath electron boundary layer under northward interplanetary magnetic field: Implications for high-latitude reconnection
Balogh, A.; Thomsen, M. F.; Lavraud, B. +7 more
We analyze Cluster data to explore the statistical properties of the magnetosheath electron boundary layer, observed outside the high-latitude dayside magnetopause, under northward interplanetary magnetic field (IMF). We investigate the dependence of the presence and directionality of heated magnetosheath electrons in this layer on the geomagnetic…
Deep Impact Observations by OSIRIS Onboard the Rosetta Spacecraft
Keller, Horst Uwe; Hviid, Stubbe F.; Lamy, Philippe +9 more
The OSIRIS cameras (optical, spectroscopic, and infrared remote imaging system) onboard the European Space Agency's Rosetta spacecraft observed comet 9P/Tempel 1 for 17 days continuously around the time of NASA's Deep Impact mission. The cyanide-to-water production ratio was slightly enhanced in the impact cloud, compared with that of normal comet…
Discovery of a bright quasar without a massive host galaxy
Wisotzki, Lutz; Jablonka, Pascale; Courbin, Frédéric +4 more
A quasar is thought to be powered by the infall of matter onto a supermassive black hole at the centre of a massive galaxy. Because the optical luminosity of quasars exceeds that of their host galaxy, disentangling the two components can be difficult. This led in the 1990s to the controversial claim of the discovery of `naked' quasars. Since then,…