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We tackle the 2D models of Kuperus-Raadu and Kippenhahn-Schluter, extended by Malherbes and Priest, via the geometric methods of the theory of dynamical systems. We treat the models as phase portraits, and discuss them from the standpoint of mathematics only, without regard to physical significance. Some phase portraits are very intricated and we raise questions about them. We also suggest possible phase portraits. This paper tries to draw attention to new tools, used in celestial mechanics, as useful for the solar physics too and for a suitable interdisciplinary cooperation. [ABSTRACT FROM AUTHOR]

The heating of solar atmosphere from chromosphere to corona is one of the key fundamental and yet unresolved questions of modern space and plasma physics. In spite of the multi-fold efforts spanning over half a century including the many superb technological advances and theoretical developments (both analytical and computational) the unveiling of the subtle of coronal heating still remains an exciting job for the 21st century! In the present paper I review the various popular heating mechanisms put forward in the existing extensive literature. The heating processes are, somewhat arbitrarily, classified as hydrodynamic (HD), magnetohydrodynamic (MHD) or kinetic based on the model medium. These mechanisms are further divided based on the time scales of the ultimate dissipation involved (i.e. AC and DC heating, turbulent heating). In particular, attention is paid to discuss shock dissipation, Landau damping, mode coupling, resonant absorption, phase mixing, and, reconnection. Finally, I briefly review the various observational consequences of the many proposed heating mechanisms and confront them with high-resolution ground-based and satellite data currently available. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Hard X-ray emission during solar flares indicates usually presence of two or more sources, interpreted as regions of precipitation of non-thermal electrons propagating along the legs of the flaring magnetic loops. These sources often show asymmetry in hard X-ray fluxes. The brighter source is usually located in a weaker photospheric magnetic field region. For a simple interpretation a weaker convergence of magnetic field lines in a loop’s leg with a weaker magnetic field allows more electrons to reach the chromosphere. Another possibility is that the source of the energy release is located closer to one end of the loop. In this case this footpoint can be brighter in hard X-ray independently on the strength of the underlying magnetic field. In this paper we present example of a flare in which possible electron acceleration site is located asymmetrically, near one of the footpoint at the place where two magnetic loops interact. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Valuable results of the Romanian Solar physics research were obtained in the framework of the international collaborations. This contribution reviews the main cooperative programs as well as their results. The regular solar observations began at the Bucharest Solar Station simultaneous with the International Geophysical Year program, on June 1, 1957. At the beginning, there were carried out solar patrol observations. A long cooperation with the World Data Centers was based on the data obtained on active chromospheric phenomena as well as the relative sunspot number and the sunspot positions. A lot of solar observations were made during specific campaigns, in connection with some international programs. Collaboration projects with the solar departments from other countries were set up in the framework of the cooperation between the Romanian Academy and similar institutions from abroad. The Romanian solar physics researchers acceded to JOSO (Joint Organization for Solar Observations) from 1992 and new perspectives to collaborate were open. We also notice the Romanian participation in the COST Action 724 (2004–2007) and Balkan, Black Sea and Caspian Sea Regional Network on Space Weather Studies (2005). On the personal basis, a lot of collaborations were developed with the research centers that offered training grants and PhD or post-doctoral grants to the young Romanian scientists. [ABSTRACT FROM AUTHOR]

The Fermi Gamma-ray Space Telescope, launched in June 2008, is an international space mission dedicated to the study of the high-energy gamma rays from the Universe. The main instrument aboard Fermi is the Large Area Telescope (LAT), a pair conversion telescope equipped with the state-of-the art in gamma-ray detectors technology, and operating at energies >30 MeV. During first two months of data taking, Fermi has detected high-energy gamma rays from the quiet Sun and the Moon. This emission is produced by interactions of cosmic rays; by nucleons with the solar and lunar surface, and electrons with solar photons in the heliosphere. While the Moon was detected by EGRET on CGRO with low statistics, Fermi provides high-sensitivity measurements on a daily basis allowing both short- and long-term variability to be studied. Since Galactic cosmic rays are at their maximum flux at solar minimum we expect that the quiescent solar and lunar emission to be a maximum during the period covered by this report. Fermi is the only mission capable of monitoring the Sun at energies above several hundred MeV over the full 24th solar cycle. We present first analysis showing images of Moon and the quiet emission of the solar disk, giving a description of the analysis tools used. [ABSTRACT FROM AUTHOR]

Three projects dealing with solar diameter evolution are presently in development. Historical and contemporary eclipses and planetary transits data collection and analysis, to cover potentially the last 5 centuries with an accuracy of few hundreds of arcsecond on diameter’s measurements. The French space mission PICARD with a few milliarcseconds accuray. With PICARD-SOL instruments located at the plateau of Calern the role of the atmosphere in ground-based measurements will be clarified. CLAVIUS is a Swiss-Italian project based on drift-scan method, free from optical distortions, where hourly circles transits will be monitored with fast CMOS sensors in different wavebands. The will run at IRSOL Gregory-Coudé telescope. [ABSTRACT FROM AUTHOR]

The presence of small-amplitude oscillations in prominences/filaments is well-known from long time ago. These oscillations, whose exciters are still unknown, seem to be of local nature and are interpreted in terms of magnetohydrodynamic (MHD) waves. During last years, observational evidence about the damping of these oscillations has grown and the mechanisms able to damp these oscillations have been the subject of intense theoretical modelling. Here, we summarize some of the theoretical results obtained about the time damping of small-amplitude oscillations in prominence/corona medium. [ABSTRACT FROM AUTHOR]

Data on Baily beads observed in total eclipse of March 29, 2006 (Egypt) and those of annular eclipses of September 22, 2006 (French Guyana) and October 3, 2005 (Spain) are used to evaluate the variations of solar radius with respect to its standard value during a whole draconitic year. A portable observatory has to be set on the shadow limit of central eclipses, where lunar limb is grazing to the solar one and the number of beads is large. The observation of solar corona during Egyptian eclipse for several minutes during maximum eclipse on shadow's limits is studied in parallel with the eclipse observed by Clavius in 1567. From fall 2005 to fall 2006 the solar radius does not show significant changes (0.00 to -0.01 arcsecs) with respect to its standard value of 959.63 arcsec within errorbars of 0.17 arcsecs. This is its value at minimum of cycle 23 of solar activity. [ABSTRACT FROM AUTHOR]

The equations of stellar structure and evolution need to be solved to model the interior of the Sun. Modelling the Sun is, however, slightly more complicated than modelling other stars since we have more observational constraints for the Sun than for other stars. In this article we discuss the basics of modelling the interior structure of the Sun. We also discuss the inputs needed to construct such a model, and how we test whether the resulting solar model is correct. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Hypothetical axion-like particles with a two-photon interaction would be produced in the sun by the Primakoff process. In a laboratory magnetic field they would be transformed into X-rays with energies of a few keV. The CAST experiment at CERN is using a decommissioned LHC magnet as an axion helioscope in order to search for these axion-like particles. The analysis of the 2003 data showed no signal above the background, thus implying an upper limit to the axion-photon coupling of gaγ < 1.16 × 10-10 GeV-1 at 95% CL for ma ≤ 0.02 eV. The stable operation of the experiment during 2004 data taking allowed us to lower down this parameter to a preliminary value of gaγ < 0.9 × 10-10 GeV-1. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

X-ray observations of the solar corona have been undertaken in Solar Physics Division (Space Research Centre of the Polish Academy of Sciences, Wrocław) for more than 35 years. Short history of these observations is presented. We focus mainly on the results from the latest experiments. These are hard X-ray photometer onboard the INTERBALL-Tail Probe and two Bragg crystal spectrometers recording solar X-ray spectra from CORONAS-F satellite. Such observations provide useful information on solar coronal plasma heated up to temperatures of several 106 – 107 K. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

According to their timescale, emission from the Sun can be divided into three types. There is the slowly varying emission which changes on a timescale of 11 years and follows the solar cycle. A more rapidly varying radiation on timescale of weeks, known as quiescent emission, is related to the occurrence of active regions. Last but not least is the very abrupt emission produced by solar activity such as flares and coronal mass ejections on timescales of second to hours. All three kinds of behavior can also be observed at radio wavelength, each being produced mostly by different mechanisms. At microwave and millimeter wavelengths, the quiet Sun emission, which varies on 11 years timescale, is due to thermal bremsstrahlung. Nevertheless, the quiescent radio emission has a strong contribution from thermal gyro-resonance especially at microwaves, whereas thermal bremsstrahlung dominates the millimetric and submillimetric waves. On the other hand, gyro-synchrotron radiation from non-thermal electrons is the main mechanism producing the flare emission at wavelengths shorter than cm, whereas the metric and decimetric emission from radio burst are due to coherent plasma radiation. Especial emphasis will be given to the newest findings in solar radio astronomy by the Solar Group at CRAAM. These results were obtained mainly from two radio telescopes: the Submillimeter Solar Telescope (SST) operating at 212 and 405 GHz and the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We review recent progress using numerical simulations as a testbed for development of a theory of stellar convection, much as envisaged by John von Newmann. Necessary features of the theory, non-locality and fluctuations, are illustrated by computer movies. It is found that the common approximation of convection as a diffusive process presents the wrong physical picture, and improvements are suggested. New observational results discussed at the conference are gratifying in their validation of some of our theoretical ideas, especially the idea that SNIb and SNIc events are related to the explosion of massive star cores which have been stripped by mass loss and binary interactions [1] [ABSTRACT FROM AUTHOR]