The ultrashort period dwarf nova SW ursae majoris

SW UMa is an unusual dwarf nova in several respects. Recent observations by Robinsonet al. (1986) have established that SW UMa is an SU UMa system, while Shafter, Szkody, and Thorstensen (1986) have presented evidence suggesting that SW UMa may be a DQ Her system as well. If the DQ Her classification is confirmed then SW UMa will be the only system to have this dual classification. Finally, time resolved spectroscopy of SW UMa has revealed the presence of an S-wave component in the H emission which has an unexpected phasing relative to the line wings.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.     

Age distribution of open clusters as a function of their linear diameter and age-dependence of cluster masses

From the well-observed data of star clusters, the age distribution of galactic clusters is obtianed as a function of their linear diameter and it is concluded that the observed age distribution of clusters for different linear diameter intervals within 1500 pc, is not seriously affected by the selection effects. If we assume that the rate of formation of clusters is constant, the lifetimes _1/2 of the clusters for different linear diameter intervals have been obtained and it is found that the clusters with a linear diameter in the range 0–1.9 pc have longer lifetimes than the clusters having linear diameters larger than 2.0 pc.Total masses of 57 clusters have been obtained using the catalogues of Piskunov (1983) and Myakutinet al. (1984). A study of age-dependence of cluster masses, based on the total masses of the clusters obtained in the present study and the cluster masses given by Bruch and Sanders (1983) and Lynga (1983b), shows that there is a decreasing trend in the total mass with the age, however, there is an increasing trend after the age of about 10⁸ yr. It is also concluded that the initial rate of formation of rich clusters was relatively higher than the present rate of formation.     

Implications from the shape of the viscosity-surface density relation

We present results of new vertical structure computations for cool, convective accretion disks. The influence of the uncertainty in the low temperature opacities on the cool branch of the viscosity-surface density relation is investigated. We discuss how the shape of this relation allows a prediction of temperatures in the accretion disk during the onset of an outburst and we compare this with observations for VW Hydri by Hassall (1984).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.     

Microstructures in type III events in the solar wind

A model is presented for the generation and evolution of bump-in-tail driven Langmuir waves in the solar wind during type III emission, which removes a number of apparent inconsistencies between theory and observations. It is argued that there must be localized enhancements of f _b /v by a factor of 10² over the measured average values. Growth rates and energy densities of Langmuir waves are, therefore, considerably enhanced, permitting growth to overcome linear scattering losses, and also allowing nonlinear decay into ion-acoustic waves, in line with observations. Estimates are made of the probability distribution p(E), of wave field strengths E, based on linear and nonlinear wave-packet evolution, yielding p(E) E ^–a, 3. This helps explain why very high values of E are rarely found in the measured spiky wave turbulence.     

Hydrogen emission from moving solar prominences

Brightness variations of the lines arising from a five-level hydrogen model atom, depending upon prominence velocities, have been investigated using a combination of two non-LTE techniques. The importance of the Doppler brightening and/or Doppler dimming effects is demonstrated for the lines of the Lyman and Balmer series.On leave from Wroclaw University Observatory, Poland.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Sunspot umbral oscillations in Mgii k

Time series observations of the profile of the Mgii k line 2795.52 have been obtained in five sunspots with the Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission. The three sunspots with umbrae larger than the 3 × 3 pixel size show significant oscillations in integrated line intensity and line centroid, with frequencies in the range 5.29–7.55 mHz (periods of 132–190 s).The frequencies of significant peaks in average umbral power spectra agree well with the frequencies of the three lowest-frequency transmission peaks predicted by a model of resonant transmission of acoustic waves. If radiative delays are unimportant, and the line centroid can be interpreted straightforwardly as a Doppler shift, the measured velocity-intensity phase differences indicate the superposition of upward- and downward-propagating waves in the umbral chromosphere; this is further evidence for the resonant transmission model.A single, quiet Sun time series of k core profiles yields power spectra and a phase difference consistent with the existence of a chromospheric p-mode.The SMM data used in this work were available only because of the repair of the SMM spacecraft by the crew of Challenger on mission 41-C. The pilot for that mission and the commander of Challenger's last mission was Francis R. Scobee.This work is dedicated to his memory.     

The dynamo dilemma

The recent determination that the angular velocity of the Sun declines downward through the convective zone raises serious questions about the nature of the solar dynamo. The principal qualitative features of the Sun are the azimuthal fields that migrate toward the equator in association with an oscillating poloidal field which reverses at about the time of maximum appearance of bipolar magnetic regions. If decreases downward, or is negligible, the horizontal gradient in produces a dynamo with some of these essential characteristics. There is reason to think that the dynamo is confined to the lower half of the convective zone where has the opposite sign from the usual ( > 0 in the northern hemisphere) producing equatorward migration but reversing the sign of the associated poloidal field. Meridional circulation may play an essential role in shaping the dynamo. At the present time it is essential to measure accurately and determine the nature of the meridional circulation.Solar Cycle Workshop Paper.     

Evidence for interacting loop process in a phase of the May 16, 1981 flare

The behaviour of the flare in the period of enhancement and maximum of hard X-ray, microwave and decimetric type IV continuum is analysed. The elongation of the H ribbons and microwave source disclose that the energy release site was shifting through a system of loops with a velocity less than 200 km s^-1, and that the energy was carried down the field lines with a velocity of about 1000 km s^-1, implying the thermal conduction front mechanism of energy transport. Several processes of energy release are considered and it is concluded that an explanation in terms of succeeding interactions of neighbouring loops, involving fast reconnection of their poloidal components is in best agreement with the observations.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.     

Sur l'existence de certaines configurations d'equilibre relatif dans le probleme desN corps

Résumé On sait que les positions d'équilibre relatif dans le problème des trois corps, où les corps se trouvent aux sommets d'un triangle équilatéral, existent lorsque les masses sont quelconques; tandis que pourn=4 (voir [3]) et pourn=5 (voir [4]), les positions d'équilibre relatifs, où les corps se trouvent aux sommets d'un polygone régulier de n cotés, existent seulement si les masses sont égales. L'objet de cet article est de montrer que ce dernier résultat est vrai pour toutn4.

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It is known that in the three body problem, the equilateral configuration of relative equilibrium exists for all values of masses, while in then-body problem, forn=4 (see [3]) andn=5 (see [4]), the position of relative equilibrium where the bodies are at the vertices of a regular polygon withn sides, exists only if the masses are equal.We prove in this paper, that this last result is true for alln4.