Evidence for a low-density inflationary universe?

The inflationary unvierse model predicts the density parameter ₀ to be 1.0 with the cosmological constant ₀ usually taken to be zero, whereas observational estimates give ₀0.2 and ₀10^-57 cm^–2. It was found, however, that the observed variation of angular diameter with redshift for extragalactic radio sources could be interpreted in terms of a low density universe with linear size evolution of the sources for either an inflationary model with 0 or an open model with =0.     

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.     

Unsteady hydromagnetic flow through a porous medium between two infinite parallel porous plates with time-varying suction

Unsteady two-dimensional flow of a viscous incompressible and electrical-conducting fluid through a porous medium bounded by two infinite parallel plates under the action of a transverse magnetic field is presented when there is time-varying suction at the plates. The lower plate is at rest while the upper plate is oscillating in its own plane about a constant mean velocity. Expressions for the velocity, fluctuating parts of the velocity, amplitude, and phase of the skin-friction are obtained. The flow phenomenon has been characterized by the parametersK (permeability of the porous medium),N(magnetic parameter) (frequency parameter), andA(variable suction parameter) and the role of these parameters on the flow characteristics has been studied.     

Magnetic reconnection in high-temperature plasma of solar flares

Quasi-steady high-temperature current sheets are an energy source during the main or hot phase of solar flares. Such sheets are shown to be stabilized with respect to the tearing instability by a small transverse component of magnetic field existing in the sheets.     

Large-scale structure of background fields and active regions

An attempt is made to study the relations between emergence of active regions and the solar background large-scale structures on the basis of Solar Geophysical Data, including Kitt-Peak magnetograms, H filtergrams, and Ca images.The emergence of 217 active regions (a.r.s) that have appeared on the solar disk not farther than ± 60° from the central meridian is studied. The a.r.s are divided into two classes A and B according to their birth location. Class A contains a.r.s emerged far (8–10°) from the background field boundaries, and class B- those emerged near to (55°) or just at the boundaries.It was found that a.r.s of class A differ appreciably from those of class B; in particular, the dimensions and the intensity (S, I) of class B a.r.s are nearly twice as large as those of class A. For class A a.r.s some alterations of the solar large-scale structure boundaries were found in 15% of all the cases, whereas for those of class B in 60%.     

Unstable chromospheric dark features and type-III bursts association

The temporal association between the kinematic parameters of chromospheric dark features (DF) and the production of radio type-III bursts is investigated during a period of five months. The Doppler shifts inside six different DF are measured by means of the Meudon Multichannel Subtracting Double Pass Spectrograph (MSDP) during periods of some minutes around 24 type-III bursts. The position of the radio bursts has been checked to be associated with the same active region observed by MSDP, by using the Nançay Radioheliograph. It appears that 23 out of 24 bursts take place when the DF is totally or predominantly blue-shifted. In 18 out of 21 cases, a maximum of the outward velocity is observed in the optical image closest in time to the radio burst. The following peculiarities are also shown by the analyzed DF:

1. All of them present a lengthened shape, in most cases pointing toward a sunspot: a bright region coinciding with a parasitic polarity is observed in between.
2. Horizontal velocities along the DF major axis are often observed, always in a direction opposite to the sunspots.

This association is interpreted by assuming that a shock wave, generated by the moving chromospheric material, is able to accelerate coronal electrons (according to a mechanism proposed by Leroy and Mangeney, 1984) thus producing type-III bursts.     

An UV survey of the galactic plane

The present paper is the introduction to a systematic analysis of 123 6-degree fields near the galactic plane, recorded in the medium ultraviolet (2000 Å) by the ballon-borne experiment SCAP 2000 of the Laboratoire d'Astronomie Spatiale, Marseille, and Geneva Observatory. The available data are presented and the general properties of the images are briefly discussed.It is shown that the high selectivity of the UV passband regarding spectral type, together with the strong interstellar extinction at that wavelength, provide the necessary conditions for an efficient application of Wolf's method to study the distribution of interstellar matter in the solar neighbourhood. The results of a fast analysis of the available data are presented here.     

Hydrodynamical models of type II supernovae

A series of hydrodynamical models of type-II supernova outbursts (SNII) has been calculated. Approximate relations connecting the total outburst energy ε, the mass of envelope ejectedM, the presupernova radiusR, and the amount of ionizing quanta radiated by the supernovaeN _H with such values as the duration of the light curve plateau Δt, and absolute magnitude in the wavelength bandV and photospheric velocityU _PH observed near the middle of the plateau have been established. Advantage has been taken of the relations to obtain a preliminary evaluation for the characteristics of the average SN II: ε=7×10⁵⁰ erg,M=6M _⊙,R=500R _⊙,N _H=2×10⁵⁸. The SNIIs with plateau-like light curves seem to be accounted for by thermonuclear explosions of degenerate cores of red giant stars and result in a total disruption of the star without any stellar remnant. To the contrary, SNIIs with linear light curves have substantially different properties (in particular, they throw considerably less massive envelopes off). These SNII must signify the birth of collapsed objects—neutron stars (pulsars) or black holes.     

Preliminary observations of solar radio sources with the Culgoora radioheliograph operating at four frequencies

The Culgoora radioheliograph has been modified for observing at 327.4 MHz, which is in addition to the three frequencies (43.25, 80, and 160 MHz) previously available. At the new frequency the array beamwidth is 56, which represents the highest resolution yet available for metre-wavelength solar mapping.At 327.4 MHz the sources of radio emission are mainly in the lowest layers of the corona. Some preliminary four-frequency observations have been made of type I storms. It is found that the source size generally decreases with increasing observing frequency. This result confirms earlier suggestions that the sources of both type I and type III emission are contained in structures whose boundaries diverge outwards in the corona.