Hα Photometry of Two Contact Binaries

We carried out optical and Hα photometry of two contact binaries (V861 Herculis, EQ Tauri). The light curve modeling revealed stellar spots in both contact systems and strong Hα excess in the position of the observed stellar spots. A correlation was found between the V−R and R−H_α colour indices of V861 Her.     

Bi-dimensional observation of waves near the mesopause at auroral latitudes

During a campaign of optical observations at high latitude, a bi-dimensional study of the wave structure of the OH layer has been performed in December 1981 from Sodankyla (Finland). This site is one of the three stations of the EISCAT ionosphere sounding system. It has been found that a wave field covering an area of 1 million km² may extend to latitudes as high as 70°N. The OH wave structure shows many similarities with noctilucent clouds. The fairly large horizontal wavelength, of the order of 40 km cannot easily be explained by a wave motion at an interface. The observed wave structure seems to be a result of the propagation of an internal gravity wave in the 80–100 km region. This wave structure was often recorded during the same time as an active aurora was present. As a result, it appears that the perturbation might be correlated with particle precipitations at auroral latitudes.     

Direct generation of solar and stellar radio bursts by energetic electron maser

A fully relativistic electron maser is proposed for the explanation of certain non-thermal solar and stellar radio bursts. This mechanism (maser synchrotron) is based on a gyroresonant interaction between waves and electrons of high energies and uses the free energy contained in an electronic distribution function that peaks for energies around 1 MeV.By a calculation of the growth rates of the three electromagnetic modes, we show that the X-mode prevails for values of _p/ _cup to 2 or 3. This result is very different from the standard cyclotron maser case where such values of _p/ _clead to quench the X-mode growth. Hence, the synchrotron maser instability appears to be a direct and efficient amplification process for considerably larger physical conditions than the cyclotron maser. In addition, the radiation, emitted over the second gyroharmonic, freely propagates without a strong reabsorbtion at the 2 _clayer. All these points can constitute major advantages of this mechanism in an astrophysical context.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.     

Secular resonances: New results

We integrated numerically, in the frame of the four body problem Sun-Jupiter-Saturn-asteroid the orbit of the asteroid 1974 MA, an Earth-crosser, which is located in a region where three resonances overlap: the two secular resonances ₅ and ₁₆ and the mean motion resonance 5/1. The numerical integration yields a qualitative orbital evolution of this particular region.     

Littoral '92

Reports

Littoral '92     

African linkage of Precambrian Sri Lanka

New age and isotopic data show that the high-grade basement rocks of Sri Lanka were not linked to the Archaean granulite domain of southern India but experienced their main structural and metamorphic development during the Pan-African event some 950 to 550 Ma ago. This occurred when West Gondwana and East Gondwana collided to form one of the longest collisional structures in the Supercontinent — the Mozambique belt that extends from Mozambique to Ethiopia and Sudan. A major tectonic boundary, interpreted as a thrust zone, divides the Highland/Southwestern Complex in the central part of Sri Lanka from the Vijayan Complex in the E and SE. The former is interpreted to represent the remnant of a once extensive passive margin extending west, in a Gondwana reconstruction, via Madagasgar to Tanzania and Mozambique. The Vijayan Complex may have been part of a separate continental margin plutonic assemblage, and its collision with the Highland/ Southwestern Complex marks the final amalgamation of East and West Gondwana into a supercontinent some 550 Ma ago. The Sri Lankan granulites cannot be correlated with the distinctly older granulites of the Eastern Ghats belt of India, and this suggests that Sri Lanka was situated close to the SE coast of Madagascar in a Gondwana reconstruction.

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Zusammenfassung Neue Isotopen- und Altersdaten aus dem metamorphen Grundgebirge von Sri Lanka zeigen, daß dieses Gebiet nicht, wie vielfach vermutet, Teil des archaischen Granulitkomplexes von Südindien war, sondern seine strukturelle und metamorphe Entwicklung während der panafrikanischen Orogenèse zwischen ca. 950 Ma und ca. 550 Ma hatte. Diese Orogenèse ist das Resultat der Kollision zwischen West-Gondwana (Afrika und Südamerika) und Ost-Gondwana (Südindien, Australien und Antarktis) und führte zur Bildung eines der längsten Kollisionsgürtel des Superkontinentes, dem Mosambik-Gürtel, der sich von Mosambik bis nach Äthiopien und in den Sudan erstreckt. Der West- und Zentralteil Sri Lankas mit den Wanni und Highland/Southwestern Komplexen wird vom Vijayan Komplex im Osten und Südosten durch eine Überschiebungszone getrennt, die möglicherweise eine Sutur darstellt. Die Gesteine im Westen und in den Highlands werden als der Rest eines ehemals weiträumigen passiven Kontinentalrandes interpretiert, zu dem wohl auch die lithologisch ähnlichen Abfolgen der hochmetamorphen Gebiete in Mosambik, Tansania und Madagaskar gehörten. Der Vijayan Komplex war wohl Teil der separaten plutonischen Suite eines aktiven Kontinentalrandes, und seine Kollision mit dem Highland/ Southwestern Komplex markiert das endgültige Verschweißen von West- und Ost-Gondwana zu einem Superkontinent vor ca. 550 Ma. Die Granulite Sri Lankas können nicht mit den deutlich älteren Granuliten des Gürtels der Eastern Ghats in Südost Indien korreliert werden sondern ähneln eher den hochgradigen Gesteinen in Südost Madagaskar. Damit ist die Lage Sri Lankas nahe Madagaskar in einer Gondwana Rekonstruktion wahrscheinlicher als nahe der Südostküste Indiens.

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Résumé De nouvelles données isotopiques et géochronologiques montrent que les roches métamorphiques du socle du Sri Lanka ne constituent pas, comme on l'a souvent cru, une partie du complexe granulitique archéen de l'Inde méridionale, mais qu'elles ont vécu leur propre histoire tectono-métamorphique au cours de l'orogenèse panafricaine, entre 950 et 550 Ma. Cette orogenèse est le résultat de la collision entre le Gondwana occidental (Afrique et Amérique du Sud) et le Gondwana oriental (Inde du sud, Australie et Antarctique) et constitue une des plus grandes chaînes de collision du Supercontinent: la chaîne du Mozambique, qui s'étend du Mozambique jusqu'au Soudan et en Ethiopie. Un contact tectonique majeur, interprété comme un charriage, sépare le »Highland/South-western Complex« (partie centrale du Sri Lanka) du »Vijayan Complex« (partie est et sud-est). Le premier de ces complexes est interprété comme un reste d'une ancienne marge passive de grande étendue, à laquelle appartenaient aussi les séries lithologiquement analogues du domaine très métamorphique du Mozambique, de Tanzanie et de Madagascar. Le «Vijagan Complex« a pu être une partie d'un ensemble plutonique séparé de marge active; sa collision avec le »Highland/Southwestern Complex« marque la réunion finale en un super-continent il y a quelque 550 Ma, des Gondwanas oriental et occidental. Les granulites du Sri Lanka ne peuvent pas être corrélées avec celles de la chaîne des Eastern Ghats (Inde du sud-est) qui sont nettement plus anciennes; elles se rapprochent plutôt des roches très métamorphiques du sud-est de Madagascar. On en déduit que la position du Sri Lanka, dans une reconstruction du Gondwana, devait être plus proche de Madagascar que de la côte sud de l'Inde.

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Diurnal photometric conditions at Teide observatory and long-term solar irradiance variations

Monochromatic extinction coefficients at four wavelengths have been obtained over a period of more than two years at the Observatorio del Teide (Izaña Tenerife) using a full disc, direct sunlight, quadruple photometer devoted to the detection of integral luminosity oscillations of the Sun. The mean extinction coefficients (0.13 at 500 nm) show a seasonal variation of about 15%, the best atmospheric conditions being in winter and autumn. Moreover, in anyone day the extinction coefficient in the afternoon is always lower than the one in the morning by 7%. A one-year period fluctuation, with an amplitude of 0.035 mag, has been identified in the instrumental magnitudes outside the atmosphere, and is interpreted as the variation produced by the different Sun-Earth distance from winter to summer. Finally, the study made to detect periodic time fluctuations in both, Sun's magnitude and extinction coefficients, has given null results at levels of 0.04 and 1.8%, respectively.     

The 1 Mpc giant head-tail radio galaxy IC 711: 3-dimensional simulation and additional constraints on the ram pressure theory

Recent observations of the longest known head-tail galaxy IC 711, at long wavelengths have shown it to extend farther than previously known. At δ 74 cm, Vallée and Roger (1987) found it to stretch 17′ (930 kpc) behind the optical nucleus of this elliptical galaxy. At δ92 cm, Vallée and Strom (1988) found it to stretch 18.3′ (1 Mpc) behind the optical nucleus. What new physics can be learned from it? To that end, a theoretical simulation in 3 dimensions of the longest head-tail galaxy has been performed, building the radio trail cell by cell inside a volume of space composed of 8 million cells, with each cell being assigned a proper radio emissivity. Matching ram pressure theory and recent observations yields a primary fast decrease of the radio luminosity with time or distance from the optical nucleus of the galaxy, and a secondary periodic variation of the radio luminosity every 500 kpc. Near the end of the tail, a sudden and unpredicted flare-up of the observed width of the tail requires a sudden change in the jet's physical conditions about 2 Gyr earlier, or that of the surroundings. These simulations provide some additional constraints on the ram pressure theory. Along the tail ridge, particle aging and particle acceleration must combine to give a luminosity function that mimics an exponential decrease with time. Across the tail ridge, no edge brightening is necessary, suggesting that particle aging and particle acceleration must combine via central turbulences and central instabilities (not by edge effects). The disappearance of the radio trail at two points along the radio ridge is unexpected from the ram pressure theory. Thus particle aging and particle acceleration must combine once more to mimic a sinusoidal modulation with time of the radio luminosity, perhaps near the nucleus inside the optical galaxy.