An observational study of a spotted W UMa-type binary star CK Bootis

New photoelectric observations of CK Bootis (a binary star suspected of a spot activity) obtained in 1988 at Mt. Suhora Observatory are presented. On the basis of the spectroscopic observations made in May 1990 at the Toru University Observatory the spectral class F6V of the primary component was estimated. The physical parameters of the system with a circular spot were derived making use of the Wilson-Devinney code.     

Definition of the large-scale extinction — A new solution of the central void phenomenon

The Estonian School results (Jõeveeret al., 1977) concerning the galaxy cell structure were partly interpreted in the spirit of Zwicky's idea on intergalactic dust, although it remained a speculation. The same view was proposed also by Rudnicki to explain the evident deficit of galaxies in the central region (Central Void) of the Jagellonian field. (Ziba (1974) tried to explain the effect of the central void in terms of an interstellar obscuration.) This explanation of the central void (CV) in terms of a possible intergalactic dust was opened up again inNuovo Cimento, 1984 and 1985; and its merits considered by Rudnickiet al. inComments on Astrophysics, 1989. Now we present a new solution of the problem of the CV mystery.     

Certain cosmological models and a new principle of equivalence

In this paper we prove an equivalence of velocity and Bellert's dilatation of metric. It is the kind of principle such as the equality of gravitational and inertial masses, noted by Newton, or equivalence of acceleration and space curvature, proved by Einstein. Our equivalence can be a foundation of a new theory, as it was in the two mentioned cases.The result is presented in two ways. One of these is a comparison of cosmological theories; and a dependence between the most important cosmological models is obtained. In this paper one of the results from the previous paper of the author (Rydzyska, 1989) is corrected.     

The ice/bed interface mosaic: deforming spots intervening with stable areas under the fringe of the Scandinavian Ice Sheet at Sampława,Poland

The glacial sediment succession exposed close to the southern margin of the Late Weichselian Scandinavian Ice Sheet in Poland reveals a mosaic consisting of isolated patches of heavily deformed deposits separated by areas lacking any visible evidence of deformation. In the studied outcrop, the subglacial deforming spots composed of outwash deposits intercalated with till stringers are about 2–10 m wide and 20–60 cm thick. They rest on outwash sediments and are covered by a basal till. Based on structural and textural characteristics, the deforming spots are interpreted as previous R‐channels filled with meltwater deposits. Lack of deformation in outwash sediment immediately beneath the deforming spots and in the intervening areas between the channels suggests that the ice‐bed was frozen and the deformation of the channel infill was facilitated by high pore‐water pressure arising because water drainage into the bed was impeded by permafrost. Channel infill deposits and the till immediately above were coevally deformed to a strain of less than 9. This study documents the possible co‐existence of deforming and stable areas under an ice sheet, generated by spatially varying thermal and hydrological conditions affecting sediment rheology.     

Formation of voids in the Universe within the Lemaître–Tolman model

We develop models of void formation starting from a small initial fluctuation at recombination and growing to a realistic present-day density profile in agreement with observations of voids. The model construction is an extension of previously developed algorithms for finding a Lemaître–Tolman metric that evolves between two profiles of either density or velocity specified at two times. Of the four profiles of concern (those of density and velocity at recombination and at the present day), two can be specified and the other two follow from the derived model.
We find that, in order to reproduce the present-day void density profiles, the initial velocity profile is more important than the initial density profile.
Extrapolation of current cosmic microwave background (CMB) observations to the scales relevant to protovoids is very uncertain. Even so, we find that it is very difficult to make both the initial density and velocity fluctuation amplitudes small enough and still obtain a realistic void by today.     

On the influence of cooling and heating processes on the Parker instability – II. Numerical simulations

We investigate the Parker instability (PI) influenced by thermal processes in a non-adiabatic, gravitationally stratified interstellar medium and discuss a model including the photoionization heating together with the supplemental heating mechanisms postulated by Reynolds, Haffner and Tufte. A cooling rate due to radiative losses is described by an approximation to the realistic cooling function of Dalgarno and McCray for ionized interstellar gas. An unperturbed initial state of the system simultaneously represents both a magnetohydrostatic and thermal equilibrium, and is thermally stable. We perform a set of 3D numerical magnetohydrodynamic simulations using the zeusmp code. We find that PI developing in the presence of non-adiabatic effects promotes a transition of gas in magnetic valleys to a thermally unstable regime. We find that the region of initially enhanced density due to PI starts to condense more as the result of thermal instability action. The density in this region rises above the classical isothermal limit of two times the equilibrium value at the mid-plane. The maximum density in an evolved system reaches 10–40 times the equilibrium value at the mid-plane, and the structures so formed attain oval shapes. These results lead to the conclusion that PI, operating in the presence of realistic cooling and heating processes, can trigger the formation of dense clouds, which may give rise to giant molecular complexes.     

Evaluation of the thermal conductivity of sandstone solid skeleton using the concept of equivalent microstructure

Acta Geotechnica - We evaluate thermal conductivity of the skeleton of porous sandstone from the measurements of the effective thermal conductivities of dry and saturated specimens provided by...     

Clogging microstructures in the vadose zone—laboratory and field studies

Long-term water infiltration into porous media, like clastic deposits, causes colmatage (clogging), which is expressed by the decrease of permeability. It is caused by progressive filling of pore spaces with fine particles carried in suspension (mechanical colmatage) and minerals precipitated from water (chemical colmatage or biochemical colmatage, when the process is affected by bacterial activity). Although this material is introduced into the sediment after deposition, it does not destroy the primary framework of it but it only coats grains and fills voids. This process results in some characteristic microstructures that are called ‘clogging microstructures’. The research included: (1) experiments on sands exposed to mechanical colmatage in laboratory conditions, which aimed to describe clogging microstructures and to examine the effects of grain size distribution on the rate and degree of clogging; (2) field and laboratory studies of deposits in which colmatage occurred in natural conditions in the infiltrating water intake ‘Dębina’ in Poznań, Poland. The main goal of the research was to identify post-depositional changes that took place in fluvial deposits affected by forced river water infiltration in the Warta River valley. Examples are presented of clogging microstructures formed in deposits affected by colmatage in the laboratory and in natural conditions.

Long Secondary Periods in variable red giants

We present a study of a sample of Large Magellanic Cloud red giants exhibiting Long Secondary Periods (LSPs). We use radial velocities obtained from VLT spectral observations and MACHO and OGLE light curves to examine properties of the stars and to evaluate models for the cause of LSPs. This sample is much larger than the combined previous studies of Hinkle et al. and Wood, Olivier & Kawaler.
Binary and pulsation models have enjoyed much support in recent years. Assuming stellar pulsation, we calculate from the velocity curves that the typical fractional radius change over an LSP cycle is greater than 30 per cent. This should lead to large changes in T _eff that are not observed. Also, the small light amplitude of these stars seems inconsistent with the radius amplitude. We conclude that pulsation is not a likely explanation for the LSPs. The main alternative, physical movement of the star – binary motion – also has severe problems. If the velocity variations are due to binary motion, the distribution of the angle of periastron in our large sample of stars has a probability of  1.4 × 10⁻³  that it comes from randomly aligned binary orbits. In addition, we calculate a typical companion mass of  0.09 M_⊙  . Less than 1 per cent of low-mass main-sequence stars have companions near this mass  (0.06–0.12 M_⊙)  whereas ∼25–50 per cent of low-mass red giants end up with LSPs. We are unable to find a suitable model for the LSPs and conclude by listing their known properties.