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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,…
The extended Hα-emitting filaments surrounding NGC 4696, the central galaxy of the Centaurus cluster
Fabian, A. C.; Sanders, J. S.; Crawford, C. S. +1 more
We present images of NGC 4696, the central galaxy in the Centaurus cluster, showing the large extent of cool filaments that are bright in Hα line emission. These filaments share the detailed structure of both the central dust lane and the inner regions of the arc-like plumes seen in soft X-ray emission. The X-ray gas is at its coolest and most abs…
Three XMM-Newton observations of the anomalous X-ray pulsar 1E 1048.1-5937: Long term variations in spectrum and pulsed fraction
Tiengo, A.; Mereghetti, S.; Stella, L. +4 more
We report the results of a recent (July 2004) XMM-Newton Target of Opportunity observation of the Anomalous X-ray Pulsar 1E 1048.1-5937 together with a detailed re-analysis of previous observations carried out in 2000 and 2003. In July 2004 the source had a 2-10 keV flux of 6.2 × 10-12 erg cm-2 s-1 and a pulsed fra…
The Hubble constant from the gravitational lens CLASS B0218+357 using the Advanced Camera for Surveys
Jackson, N.; Browne, I. W. A.; York, T. +2 more
We present deep optical observations of the gravitational lens system CLASS B0218+357, from which we derive an estimate for the Hubble constant (H0). Extensive radio observations using the VLA, MERLIN, the VLBA and VLBI have reduced the degeneracies between H0 and the mass model parameters in this lens to one involving only t…
Cloud Structure and Physical Conditions in Star-forming Regions from Optical Observations. II. Analysis
Andersson, B. -G.; Federman, S. R.; Sheffer, Y. +1 more
To complement the optical absorption line survey of diffuse molecular gas in Paper I, we obtained and analyzed far-ultraviolet H2 and CO data on lines of sight toward stars in Cep OB2 and Cep OB3. Possible correlations between column densities of different species for individual velocity components, not total columns along a line of sig…