The energy distributions of magnetic variables: The effects of inhomogeneous accretion columns

Previous shock models for the AM Herculis-type magnetic variables have assumed homogeneous accretion columns, with constant infall densities out to a characteristic column radius. The resulting energy distributions are strongly peaked in the visible to ultraviolet and are in disagreement with observations. We report the preliminary results of calculations with more general radial functions of the infall density. Exponential and gaussian profiles yield continua profiles produce continua which are flatter and in better agreement with observations. Comparisons are made to data for AM Her and E2003+225.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

X-ray and ultraviolet observations of AG Draconis during quiescence and outburst

We describe the first X-ray monitoring of a symbiotic star during phases of enhanced activity. AG Dra is a Pop II object with a composite spectrum, characterized by a cool K-type component, prominent high ionization emission lines and a strong UV continuum which is attributed to a hot dwarf companion. Periodic variability of the UV radiation during minimum could be attributed to the orbital motion of the system. In April 1980 HEAO-2 detected an intense, soft X-ray flux from AG Dra, stronger than in other symbiotic stars. After one major outburst of November 1980, which continued until 1983, two more outbursts occurred in February 1985 and January 1986, and coordinated X-ray (EXOSAT) and ultraviolet (IUE) observations were organized to study the behaviour of AG Dra during different activity phases. EXOSAT observations made during decline after the 1985 outburst, revealed a weak X-ray flux in the Thin Lexan filter of the Low Energy dedtector. Observations made during minimum, in June and November 1985, at phases 0.22 and 0.50 of the UV light curve, disclosed the presence of an intense X-ray flux, which was not occulted in November. AG Dra was again observed with EXOSAT in February 1986 when the stellar luminosity was still at maximum. No X-ray flux was detected, in spite of the prominent, high ionization UV spectrum observed with IUE.A detailed discussion of the X-ray and ultraviolet results on AG Dra in the light of possible models is in progress.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Model of geomagnetic paleosecular variations for the Northern Hemisphere

Summary A model of radial drifting and oscillating dipoles to represent geomagnetic palaeosecular variations, which showed to be appropriate for the Southern Hemisphere, is evaluated for the Northern Hemisphere. After a new fitting of some involved parameters, its theoretical results are compared with the palaeomagnetic data of Lake de Bouchet (France) and the Black Sea. A time lag between the declination and inclination profiles is observed in both cases. A good cross-correlation coefficient is obtained for the declination and inclination data.Presented at 2nd conference on New Trends in Geomagnetism, Castle of Bechyn, Czechoslovakia, September 24–29, 1990.     

High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle

Synthetic spinel harzburgite and lherzolite assemblages were equilibrated between 1040 and 1300° C and 0.3 to 2.7 GPa, under controlled oxygen fugacity (f _{O 2}). f _{O 2} was buffered with conventional and open double-capsule techniques, using the Fe−FeO, WC-WO₂-C, Ni−NiO, and Fe₃O₄−Fe₂O₃ buffers, and graphite, olivine, and PdAg alloys as sample containers. Experiments were carried out in a piston-cylinder apparatus under fluid-excess conditions. Within the P-T-X range of the experiments, the redox ratio Fe³⁺/ΣFe in spinel is a linear function of f _{O 2} (0.02 at IW, 0.1 at WCO, 0.25 at NNO, and 0.75 at MH). It is independent of temperature at given Δlog(f _{O 2}), but decreases slightly with increasing Cr content in spinel. The Fe³⁺/ΣFe ratio falls with increasing pressure at given Δlog(f _{O 2}), consistent with a pressure correction based on partial molar volume data. At a specific temperature, degree of melting and bulk composition, the Cr/(Cr+Al) ratio of a spinel rises with increasing f _{O 2}. A linear least-squares fit to the experimental data gives the semi-empirical oxygen barometer in terms of divergence from the fayalite-magnetite-quartz (FMQ) buffer:

On the practice of estimating fractal dimension

Coastlines epitomize deterministic fractals and fractal (Hausdorff-Besicovitch) dimensions; a divider [compass] method can be used to calculate fractal dimensions for these features. Noise models are used to develop another notion of fractals, a stochastic one. Spectral and variogram methods are used to estimate fractal dimensions for stochastic fractals. When estimating fractal dimension, the objective of the analysis must be consistent with the method chosen for fractal dimension calculation. Spectal and variogram methods yield fractal dimensions which indicate the similarity of the feature under study to noise (e.g., Brownian noise). A divider measurement method yields a fractal dimension which is a measure of complexity of shape.     

The extinction of starlight revisited

The rigorous Kerker-Matijevi formulae for light scattering by co-axial double cylinders are used to calculate the extinction properties of hollow organic grains. A size distribution of such particles together with iron whiskers of radii 0.01 m, silica spheres of radius 0.03 m and free aromatic molecular clusters comprised of 50–100 atoms yield excellent agreement with data on the extinction of starlight. The mass ratios of silica to organics and of iron to organics are in good accord with cosmic abundance constraints.     

Cosmological implications of BL Lac objects

It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F _obs = ^{3 +} F _intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem _v must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem _v ^corr and logZ have a good correlation.     

Realisation of a celestial system based on VLBI geodynamics programs

The relative orientations of various VLBI celestial reference frames are evaluated on the basis of coordinate differences of common sources. It is shown that an accuracy better than 0.001 can be achieved. Possible regional deformations in the different catalogues are investigated; they are found to reach a few 0.001 in some restricted zones. The application of these studies to the realisation of a combined celestial reference frame consistent with the BIH Terrestrial System is outlined.     

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.