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Magnetic helicity transport in corona and filament eruptions
Romano, P.; Contarino, L.; Zuccarello, F.
Using a 28-hour time series of line-of-sight magnetograms taken by the Michelson Doppler Imager (MDI), we determined the magnetic flux variations and the rate of magnetic helicity transport at the footpoints of a filament in active region NOAA 8375. The filament was characterized by a positive helicity change due to shearing motions in both footpo…
Positions of Uranus and Its Main Satellites
Veiga, Carlos H.; Vieira Martins, Roberto; Andrei, Alexandre H.
We present astrometric positions of Uranus and its satellites Miranda, Ariel, Umbriel, Titania, and Oberon, determined in the International Celestial Reference System, from 1758 frames observed over 105 nights between 1982 and 1998. All the positions of the satellites were reduced using secondary frames referred to the Tycho-2 Catalogue from photo…
Cosmic rays tracks on the PICsIT detector
Bird, A. J.; Segreto, A.; Bazzano, A. +3 more
Since the first in orbit activation of the PICsIT detector, frequent spikes have been noticed in its count rate. Tracks in the detector images, corresponding to the spikes, indicate that these events are generated by interaction of cosmic rays with the detector plane.
Since these events constitute a significant fraction of the instrument back…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…