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Streamers and adjacent regions observed by UVCS/SOHO: A comparison between different phases of solar activity
Romoli, M.; Spadaro, D.; Ventura, R. +1 more
UVCS/SOHO observations of the O VI resonance doublet and H I Lyα line intensities and profiles, together with measurements of the visible linearly polarized radiance, have been performed during two MEDOC campaigns in 1997 and 2000, i.e. near solar minimum and approaching the solar maximum phase, respectively. During both observational runs mid-lat…
On the nature of the unidentified solar emission near 117 nm
Bertaux, J. -L.; Wilhelm, K.; Marsch, E. +6 more
Spectral observations of the Sun in the vacuum-ultraviolet wavelength range by SUMER on SOHO led to the discovery of unusual emission features - called humps here - at 116.70 nm and 117.05 nm on either side of the He i 58.43 nm line. This resonance line is seen in the second order of diffraction, whereas the humps are recorded in the first order w…
Constraining the thermal history of the warm-hot intergalactic medium
Finoguenov, A.; Maiolino, R.; Gilli, R. +3 more
We have identified a large-scale structure traced by galaxies at z=0.8, within the Lockman Hole, by means of multi-object spectroscopic observations. By using deep XMM images we have investigated the soft X-ray emission from the Warm-Hot Intergalactic Medium (WHIM) expected to be associated with this large-scale structure and we set a tight upper …
Metallicity of mono- and multiperiodic β Cephei stars
Niemczura, E.; Daszyńska-Daszkiewicz, J.
Analyzing IUE ultraviolet spectra of β Cep pulsating stars we noticed that multiperiodic variables have a larger mean metal abundance in the photosphere, [ m/H] , than monoperiodic ones. We apply statistical tests to verify this dichotomy. We obtain that, with a large probability, the multiperiodic β Cep stars have greater values of [ m/H] . This …
A solar active region loop compared with a 2D MHD model
Gontikakis, C.; Tsinganos, K.; Petrie, G. J. D. +1 more
We analyzed a coronal loop observed with the Normal Incidence Spectrometer (NIS), which is part of the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO). The measured Doppler shifts and proper motions along the selected loop strongly indicate unidirectional flows. Analysing the Emission Measure Curves of …
Temporal variations in the magnetic network large-scale dynamics
Meunier, N.
The variation in the magnetic network large-scale dynamics is investigated using MDI magnetograms from 1996 to 2004. Cross-correlation and feature tracking techniques are used on pairs of magnetograms in order to derive the dynamics at the solar surface, including magnetic network regions. The variations for both methods are very different, the fe…
The extent of 3-min oscillations in regions other than sunspot plumes
Doyle, J. G.; Banerjee, D.; O'Shea, E. +1 more
The active region, AR0554, was observed with NIS/CDS on board SoHO to examine the extent and range of oscillations from a range of features. Among all the NIS spectral lines analysed, significant oscillations were found in Si xii 520 Å, Mg x 625 Å, O v 629 Å, and He i 522 Å. The periods of the strongest oscillations in these lines were ≈10-20 min.…
Nonradial and nonpolytropic astrophysical outflows. VII. Fitting ULYSSES solar wind data during minimum
Tsinganos, K.; Iro, N.; Lima, J. J. G. +1 more
Exact axisymmetric analytical solutions of the governing MHD equations for magnetized and rotating outflows are applied to the solar wind during solar minimum as observed by ULYSSES. Using the spacecraft data, the latitudinal dependences of physical quantities such as the density, velocity, magnetic field and temperature are analytically described…
Precession from Hipparcos and FK5 proper motions compared with current values: Reasons for discrepancies
Walter, H. G.; Hering, R.
The comparison of Hipparcos and FK5 proper motions points to an inconsistency with the correction, Δ p, of the luni-solar precession derived from VLBI and LLR observations with unprecedented accuracy. An attempt is made to explain this inconsistency of approximately -1.3 mas/yr by rotational offsets of the Hipparcos and FK5 proper motion systems. …
Large-scale dynamics and polarities of magnetic structures
Meunier, N.
A large data set of MDI magnetograms is studied in order to analyse the dependence of the global dynamics of magnetic structures on their polarity. Two complementary techniques (feature tracking and correlation tracking) are used to determine the differential rotation and meridional circulation. A faster rotation of leading polarity structures is …