Interstellar medium parameters derived from low-frequency variability

Complete infraredJ andK light curves of the RS CVn system XY UMa have been obtained at the beginning of 1989. We point out some interesting morphological changes observed in these light curves.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

The ROSAT diffuse X-ray background survey

The quality and capabilities of the ROSAT survey (0.1–2.0 keV) for the study of the diffuse X-ray background and the interstellar medium are discussed. All-sky maps created from data collected during the survey phase of ROSAT operations will greatly exceed previous surveys in spatial resolution (5 arc min pixels) and statistical significance (better than 25% for unbinned pixels). The spectral information of the survey will, in general, be greater as well. Finally, because of the survey geometry, very accurate contamination identification and background subtraction will be possible ensuring the reliability of the data.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Models of white dwarfs distorted by magnetic field and differential rotation: Numerical approach

In this paper we construct a generalized classical model of a white dwarf distorted by magnetic field and differential rotation. The numerical method, to be presented, will be implemented in a subsequent quantitative treatment of the model.     

Transmission and reflection of Rayleigh waves at a thin low velocity vertical layer: A laboratory and theoretical study

A three-dimensional ultrasonic modelling was used to study the Rayleigh waves reflected from a thin low velocity vertical layer and those transmitted through the same zone. The reflection and transmission coefficients of the Rayleigh waves have been calculated by an approximate method based on the Green function technique. Nonrigid contact boundary conditions were used for the low velocity layer modelling. A rather good correspondence between the theoretical and experimental absolute values of the reflection and the transmission coefficients was obtained. Some discrepancies between experimental and theoretical results, in particular with regard to phase shifts, may be explained by a certain inadequacy of the theoretical model to the low velocity layer investigated by the ultrasonic modelling.     

Trace gas exchange at the air/water interface: Measurements of mass accommodation coefficients

A liquid jet of 90 m diameter and variable length has been utilized to determine absorption rates and, hence, mass accommodation coefficients , of atmospheric trace gases. The compounds investigated are HCl (0.01), HNO₃ (0.01), N₂O₅ (0.005), peroxyacetyl nitrate (>0.001), and HONO (0.005). It is concluded that the absorption of these trace gases by liquid atmospheric water is not significantly retarded by interfacial mass transport. The strengths and limitations of the liquid jet technique for measuring mass accommodation coefficients are explored.     

Structure of the marine boundary layer over north western Indian Ocean during 1983 summer monsoon

The spatial variability of the structure of the lower troposphere over the northwestern Indian Ocean for the period 12th July to 2nd September, 1983 has been studied using upper air data collected during the first scientific cruise of ORV Sagar Kanya.An analysis of thermodynamic structure and kinematics of the marine boundary layer for different zonal and meridional sections revealed the following features: (a) Temperature and humidity inversions were generally absent over the study area except over a few locations in the western region; (b) Large-scale subsidence was found over the central equatorial Indian Ocean; (c) The convective activity over the western Indian Ocean was found to be moderately suppressed as compared to the eastern region; (d) The zonal and meridional components of winds along the equator and 10° N zonal section exhibited a mirror-image-like distribution.     

A time dependent model for spicule flow

A time dependent model for the flow of gas in a spicule is studied. In this model, the flow occurs in a magnetic flux sheath. Starting from hydrostatic equilibrium, the flux sheath is allowed to collapse normal to itself. The collapse induces a flow of gas along the magnetic field and this flow is identified as a spicule. A variety of sheath geometries and velocity patterns for the normal flow have been studied. It is observed that a large curvature in the field geometry and a large initial value for the normal flow are necessary to achieve spicule-like velocities. The duration for which a large velocity of normal flow is required is much shorter than the average lifetime of a spicule. It is proposed that the initial rapid collapse occurs during an impulsive spicule phase and it is the subsequent gradual relaxation of the flow which is observed as a spicule.     

The development of X-ray flare onsets near active region filaments

Skylab X-ray images of the early phases of six active region transient brightenings were compared with simultaneous H images to study the spatial relationships between filaments and the X-ray brightenings. When the X-ray loops were roughly perpendicular to the axes of the H filaments, the filaments did not disappear. X-ray loops which appeared nearly parallel to the filaments were generally associated with the disappearances of those filaments. It is suggested that the perpendicular loops correspond to the class I X-ray flares of Pallavicini et al. (1977) while the parallel loops are the early phases of their class II flares characterized in the decay phases by arcades of large loops with low energy densities. Both kinds of X-ray flares can be associated with impulsive phases.