Direct mid-IR images of Gl 2591,W51-IRS2 and S140

We present the results of direct mid-IR images of the luminous young stellar objects GL 2591, S140-IRS1, and W51-IRS2. The sources show an extended mid-IR emission at the limit of our spatial resolution indicating the presence of dense circumstellar dust disks.     

The Relationship of Green-Line Transients to White-Light Coronal Mass Ejections

We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light. Two of these events, with speeds >25 km s^-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly different appearance and is more gradual than the other two, with a projected outward speed <10 km s^-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of these events to recent X-ray observations of CMEs is briefly discussed. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702     

The lost world of the olenid trilobites

Trilobites of the Family Olenidae (Upper Cambrian to Upper Ordovidan) were closely tied to an oxygen-poor environment. They show a remarkable range of adaptations, testifying to a singular evolutionary plasticity.     

Rotation of a two-component model neutron star in the GTR

Equations are obtained for the dynamics of the rotation of a two-component model neutron star within the framework of the generai theory of relativity. It is shown that for steady rotation of the star’s normal component, Ω_c = const, the angular velocity Ω_s of the superfluid component depends on the coordinates and is Ω_c + ω, where ω is the nondiagonal component of the metric tensor. Translated from Astrofizika, Vol. 40, No. 3, pp. 403–412, August, 1997.     

Steady-state drift-dominated modulation models for galactic cosmic rays

A number of steady-state drift-dominated modulation models has been developed by the Potchefstroom modulation group. In this review a selection of these models is discussed and briefly compared. A short overview of the relevant drift theory incorporated into the models is also given.     

Does time dilation tell us the distance to gamma-ray bursts?

Since the discovery that dim gamma-ray bursts last longer on average than bright ones (time dilation) the cosmological origin of this effect has been contested by various researchers. I discuss the current status of this issue and conclude that current models for a non-cosmological time dilation only explain part of the observed phenomenon, and even then betray themselves by distinct signatures in the data. As those signatures have not been seen, the cosmological origin remains the favoured explanation of the time dilation.     

A kinetic model of gas flow in a porous cometary mantle

A numerical study of gas flow through a porous cometary mantle is presented. A kinetic model based on the well-known Test Particle Monte Carlo Method for the solution of rarefied gas dynamics problems is proposed. The physical model consists of two spatial plane regions: the condensed ice phase and a porous dust mantle. The structure of the porous dust layer is described as a bundle of cylindrical inclined channels not crossing each other. A vertical temperature gradient may exist across the dust mantle. The aim is to investigate how the characteristics of molecular flow depend on the capillary length, inclination angle, and temperature gradient. Examples illustrating a significant deviation of some results from equilibrium values are shown. In particular, the gas velocity distribution at both ends of the pore is strongly non-Maxwellian if there is an important temperature contrast across the pore. The emergent gas flow rate is found to vary with the pore length/radius ratio in excellent agreement with Clausing's empirical formula. The degree of collimation of the flow is quantitatively studied as a function of the length/radius ratio, and consequences for the jet force of outgassing through a dust mantle or, indeed, a rough surface are estimated.     

Simultaneous five color (UBVRI) polarimetry of EF Eri

We present the first observations of the AM Her type object EF Eri where both the polarization and the photometric data are recorded simultaneously in five color bands (UBVRI). The position angle rotates strongly (30°) vs. wavelength from U to I, probably due to Faraday rotation or due to fact that the polarized radiation seen in the different wavelength bands comes from different parts of the accretion region. The phase dependence of the position angle requires field and accretion geometry more complicated than a simple centered dipole and a second emitting region producing weaker intermediate pulses in the infrared seems to be present. We derive the value of the inclination of the system i=55°±5°, the colatitude of the active pole ₁,= 38° ±5° and the second emitting region = 115° ± 5°, both of which are nearly at the same longitude facing the main accretion stream.Based on observations made at the European Southern Observatory, La Silla, Chile.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.