Parallax distortion by the weak microlensing effect

Parallax measurements allow distances to celestial objects to be determined. Together with measurements of their position on the celestial sphere, they give a full three-dimensional picture of the location of the objects relative to the observer. The distortion of the parallax value of a distant source affected by weak microlensing is considered. This means that the weak microlensing leads to distortion of the distance scale. The gravitational deflection causes a retrograde apparent motion of the image, which is revealed as a negative parallax. It is shown that the distortions may significantly change the parallax values when they amount to several microseconds of arc. In particular, at this level many measured values of parallaxes should be negative.     

Celestial-mechanical peculiarities of Uranus’s satellite system

We consider the structural peculiarities of Uranus’s satellite system associated with its separation into two groups: inner equatorial satellites moving in nearly circular orbits and distant irregular satellites with retrograde motion in highly elliptical orbits. The intermediate region is free from satellites in a wide range of semimajor axes. By analyzing the evolution of satellite orbits under the combined effect of solar attraction and Uranus’s oblateness, we offer a celestial-mechanical explanation for the absence of equatorial satellites in this region. M.L. Lidov’s studies during 1961–1963 have served as a basis for our analysis.     

Damage due to ultraviolet and ionizing radiation during the ejection of shielded micro-organisms from the vicinity of 1M ⊙ main sequence and red giant stars

We present the astrophysical conditions necessary for the ejection of shielded microorganisms from a solar system and the biological conditions involving ultraviolet and ionizing radiations to which they are subjected in space. The radiation dose for both UV and ionizing radiation from the host star, the destination star and interstellar space is calculated for three different micro-organisms. The time of transport and the survival of the micro-organisms are strongly dependent on the composition and thickness of any mantle encasing the micro-organism and on the mass/luminosity ratio of the two stars. The maximum size of grains that can be ejected from the vicinity of one solar mass main sequence and red giant stars ranges from 0.65-0.35µm and 2.1-1.2µm respectively, for a reasonable range of densities. We conclude that unshielded known micro-organisms are immediately killed by ultraviolet radiation, and that an ice mantle does not provide sufficient shielding for either type of star. However, micro-organisms shielded by a carbonaceous thin-film mantle can be ejected from the vicinity of a one solar-mass red-giant star, and such micro-organisms have a high probability of surviving damage from the ultraviolet and ionizing radiations to which they are exposed.     

On the temperature measurement from the O IV emission lines

The new calculations of the Oiv temperature-sensitive EUV line ratios are presented and compared with previous results.     

High-temperature geothermal reservoir possibilities in Hungary

Theoretical studies have shown the possibility of high-temperature ('high enthalpy') geothermal reservoirs in the pre-Tertiary rocks at 4–5 km depth range within the Pannonian Basin. This expectation was proven by the hotwater/steam blowout of Fábiánsebestyén-4 borehole (16.12.85–31.1.86). Exploration efforts carried out during 1987–88 in the broad vicinity of the borehole proved that reservoirs of this type can be found with the combination of seismic reflection, silica-thermometry and magnetotelluric sounding methods. Deliberate prospection should be continued in all suitable areas within the basin, since high enthalpy reservoirs promise profitable operation of geothermal power stations.     

Scattered light models of the dust shell around HD 179821

The dust shell around the evolved star HD 179821 has been detected in scattered light in near-IR imaging polarimetry observations. Here, we subtract the contribution of the unpolarized stellar light to obtain an intrinsic linear polarization of between 30 and 40 per cent in the shell that seems to increase with radial offset from the star. The J - and K -band data are modelled using a scattering code to determine the shell parameters and dust properties. We find that the observations are well described by a spherically-symmetric distribution of dust with an r ⁻² density law, indicating that when mass-loss was occurring, the mass-loss rate was constant. The models predict that the detached nature of a spherically-symmetric, optically-thin dust shell, with a distinct inner boundary, will only be apparent in polarized flux. This is in accordance with the observations of this and other optically-thin circumstellar shells, such as IRAS 17436+5003. By fitting the shell brightness we derive an optical depth to the star that is consistent with V -band observations and that, assuming a distance of 6 kpc, gives an inner-shell radius of     , a dust number density of     at r _in and a dust mass of     . We have explored axisymmetric shell models but conclude that any deviations from spherical symmetry in the shell must be slight, with an equator-to-pole density contrast of less than 2:1. We have not been able to fit simultaneously the high linear polarizations and the small     colour excess of the shell and we attribute this to the unusual scattering properties of the dust. We suggest that the dust grains around HD 179821 either are highly elongated or consist of aggregates of smaller particles.     

Analysis of mapping coverage obtained from spacecraft

An exact analysis of the coverage obtained by spacecraft using cross-track scanning and nadir-centered conical imaging, under imposed viewing obliqueness and resolution requirements, is presented. In addition to exact expressions for the area acquired and the area acquisition rate, envelope theory is introduced to obtain the boundary of the imaged area. These expressions are relatively compact, allowing rapid machine computation. The effects of the sun phase angle, and of imaging system limitations are also examined. The Galileo mission encounter with Callisto is used as a numerical example, from which certain general conclusions are drawn regarding optimal imaging trajectories.     

Remarks on dynamical ellipticity at the Earth's

In this paper, two factors — the redistribution of the density and the variation in the angular velocity of the Earth rotation, that affect the adopted value of the flattening for equidensity surface within the Earth, are discussed. The computational results show that the contribution of the redistribution of the density in the Earth interior (especially in the core) on the change of the flattening at the core-mantle boundary (CMB) is marginal, and that the calculated value of the flattening at the CMB can be in good agreement with the VLBI observed value so long as the fact that the angular velocity of the Earth rotation has undergone the tidal evolution is taken into account. As a result, this paper presents a set of recommended values of the dynamical parameters of the Earth (see Table III) for computing Earth's forced nutation series.