Search Publications
Locations of auroral kilometric radiation bursts inferred from multispacecraft wideband Cluster VLBI observations. 1: Description of technique and initial results
Gurnett, D. A.; Pickett, J. S.; Mutel, R. L. +2 more
The Cluster Wideband Data instrument has been used to determine the locations of auroral kilometric radiation (AKR) using very long baseline interferometry. The technique involves cross-correlating individual AKR bursts from all six Cluster baselines using time and frequency filtered waveforms. The resulting differential delay peaks are used to de…
Explosive events and transition region blinkers: Time variability of non-Gaussian quiet Sun EUV spectra
Peter, H.; Brković, A.
The transition region (TR) from the chromosphere to the corona of the Sun and solar type stars is a very dynamic regime. On the Sun at least two major observational classes of transients can be seen: explosive events and blinkers. Besides these transients there is also a more steady spectral component in transition region lines that accounts for t…
On the evolutionary status of chemically peculiar stars of the upper main sequence
Paunzen, E.; Maitzen, H. M.; Pöhnl, H.
We present further evidence that the magnetic chemically peculiar stars (CP2) of the upper main sequence already occur at very early stages of the stellar evolution, significantly before they reach 30% of their life-time on the main sequence. This result is especially important for models dealing with dynamo theories, angular momentum loss during …
On the nature of the ISO-selected sources in the ELAIS S2 region
Pozzi, F.; Calabrese, E.; Gruppioni, C. +7 more
We have studied the optical, near-infrared and radio properties of a complete sample of 43 sources detected at 15 µm in one of the deeper ELAIS repeatedly observed regions. The extragalactic objects in this sample have 15-µm flux densities in the range of 0.4-10 mJy, where the source counts start diverging from no evolution models. Abo…
Low Coronal Signatures of Large Solar Energetic Particle Events
Nitta, Nariaki V.; Tylka, Allan J.; Cliver, Edward W.
We report on the low coronal signatures of major solar energetic particle (SEP) events. Because large SEP events are highly associated with both flares and coronal mass ejections, we focused on flare-associated motions in soft X-rays. In a sample of a half-dozen well-observed flares associated with SEP events, we identified two basic types of moti…
The 3-D ionization structure of NGC 6818: A Planetary Nebula threatened by recombination
Sabbadin, F.; Turatto, M.; Cappellaro, E. +2 more
Long-slit NTT+EMMI echellograms of NGC 6818 (the Little Gem) at nine equally spaced position angles, reduced according to the 3-D methodology introduced by Sabbadin et al. (\cite{Sabbadin00}a,b), allowed us to derive: the expansion law, the diagnostics and ionic radial profiles, the distance and the central star parameters, the nebular photo-ioniz…
Elemental Abundances in NGC 3516
Turner, T. J.; Kraemer, S. B.; George, I. M. +2 more
We present Reflection Grating Spectrometer data from an XMM-Newton observation of the Seyfert 1 galaxy NGC 3516, taken while the continuum source was in an extremely low flux state. This observation offers a rare opportunity for a detailed study of emission from a Seyfert 1 galaxy, as these are usually dominated by high nuclear continuum levels an…
Ultraviolet-Optical Pixel Maps of Face-on Spiral Galaxies: Clues for Dynamics and Star Formation Histories
Conselice, Christopher J.; de Grijs, Richard; Windhorst, Rogier A. +8 more
Ultraviolet and optical images of the face-on spiral galaxies NGC 6753 and NGC 6782 reveal regions of strong ongoing star formation that are associated with structures traced by the old stellar populations. We use these images to construct NUV-(NUV-I814) pixel color-magnitude diagrams (pCMDs) that reveal plumes of pixels with strongly v…
Spatial and temporal fluctuations in sunspots derived from MDI data
Solanki, S. K.; Rüedi, I.
The penumbra radiates an energy flux that is 0.75-0.8 times the photospheric value. One mechanism proposed to bring this flux to the surface is interchange convection according to which hot flux tubes rise to the surface, lie horizontally there while they cool and finally sink down again. We search for possible signatures of such a process using t…
Cassini plasma spectrometer measurements of Jovian bow shock structure
Dougherty, Michele K.; Gurnett, Donald A.; Coates, Andrew J. +9 more
The Cassini spacecraft on its way to Saturn flew by Jupiter and crossed its bow shock more than forty times on the dusk-side of the planet, whereas the early missions targeting Jupiter explored the dawnside. Here we report the first results concerning these bow shock crossings, based on the measurements of the Cassini Plasma Spectrometer (CAPS), t…