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The Quiet Sun Atmosphere as Seen by Soho
Keenan, F. P.; Phillips, K. J. H.; Gallagher, P. T. +2 more
The recent solar minimum has allowed studies to be made of quiet-Sun structures with SOHO instruments with better resolution than before. This paper reports on the morphology and dynamics of the EUV emission, including the chromospheric and transition-region network and coronal features, and how the photospheric magnetic field and coronal bright p…
Electron Density and Temperature Measurements, and Abundance Anomalies in the Solar Atmosphere
Landi, Enrico; Dwivedi, Bhola N.; Mohan, Anita
Using spectra obtained from the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrograph on the spacecraft SOHO (Solar and Heliospheric Observatory), we investigate the height dependence of electron density, temperature and abundance anomalies in the solar atmosphere. In particular, we present the behaviour of the solar FIP effect …
Coronal Mass Ejections and Large Scale Structure of the Corona
Schwenn, R.; Pick, M.; Lamy, P. +3 more
A comparative study of two events accompanied by both a flare and a CME has been performed. The data analysis has been made by comparing the observations of the LASCO/SOHO coronagraphs with those of the Nancay radioheliograph. The observations show a clear connection between coronal green and red line transient activity, burst radio emission and t…
Cooling of Energetic Particles during their Transport along Spiral Field Lines
Kóta, J.
The transport of low-energy charged particles moving along magnetic field lines is considered. We point out that particles accelerated at CIRs at larger heliocentric distances and moving inward along the spiral field lose energy and decelerate even in a purely scatter free case. This results in a sizeable reduction in intensity. Scattering increas…
A spectroscopic study of the magnetic chemically peculiar star nu Fornacis
Leone, F.; Catanzaro, G.; Malaroda, S.
The magnetic chemically peculiar star
Dynamics of Chromiospheric and Transition Region Lines Observed with SOHO/SUMER and the GCT/Tenerife
Wilhelm, K.; Schühle, U.; Foing, B. H. +3 more
High-resolution spectroscopic observations of the quiet Sun have been carried out in September 1996 at the German Gregory Coudé Telescope (GCT) in Tenerife and in May 1997 with the SUMER instrument onboard SOHO. Time sequences of spectra in the visible and near infrared as well as in the ultraviolet have been taken, covering a range of heights fro…
Coupling Between High and Low Latitudes as Observed with Lasco in the Solar Corona and in Interplanetary Space
Schwenn, R.
From Skylab, Helios and Ulysses observations we had learnt already how closely the 3D heliosphere is related to the underlying coronal structure. Around solar activity minimum, large polar coronal holes dominate the major part of the heliosphere, through the high-speed solar wind streams emanating from them. A different type of solar wind is restr…
Hard X-rays from the galactic nucleus: present and future observations
Goldoni, P.; Laurent, P.; Lebrun, F. +2 more
In spite of increasing evidences of the presence of a massive Black Hole at the Galactic Center, its radio counterpart, Sgr A*, shows little activity at high energies, and recent models involving energy advection (ADAF) have been proposed to explain this difficulty. We present results on the hard X-ray emission from the galactic central square deg…
The Hubble Constant
Mould, Jeremy
With the completion of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale, it is interesting to form the dimensionless quantity H 0 t 0 by multiplying the Hubble Constant by the age of the Universe. In a matter dominated decelerating Universe with a density exceeding 0.26 of the critical value, H…
Cosmic Ray Effects on the ISOCAM Long Wave Detector
Claret, A.; Dzitko, H.; Engelmann, J.
The ISOCAM detector is subjected to transient effects induced by cosmic rays, the so-called glitches. This paper is focused on the ISOCAM long wave detector. The predicted glitch rates have been re-evaluated by taking into account secondary particles production in the materials surrounding the LW detector. We show in this preliminary study that th…