H4 and H5 chondrites from the Rub'al Khali Desert

Abstract Al-Jimshan is a highly weathered 11.45 kg chondrite that was found in 1955 in the Rub' al Khali Desert, Saudi Arabia (20*42′N, 52*50E) about 240 km south-east of the town of al-Hadidah. The main mass is now at UCLA. Based on texture and mineral composition (olivine Fa_17.7 ± 0.4; pyroxene Fs_15.7 ± 1.0 Wo₁₃ ± 0.4), al-Jimshan is classified as an H4 chondrite of shock stage S2. The Bir-Hadi and ad-Dahbubah H chondrites, which also were found in the Rub'al Khali (Holm, 1962), are probably not paired with al-Jimshan. They are classified as H5, shock stage S3 (Fa_18.1 ± 0.5, n = 10; Fs_16.0 ± 0.6, Wo_1.1 ± 0.4, n = 9) and H5, shock stage S2 (Fa_17.9 ± 0.3, n = 10; FS_15.5 ± 0.2 Wo_1.0 ± 0.4, n = 10), respectively.     

Diffusion of elements in the interstellar medium in early-type galaxies

The role of diffusion in the redistribution of elements in the hot interstellar medium of earlytype galaxies is considered. It is well known that gravitational sedimentation can affect significantly the abundances of helium and heavy elements in the hot intergalactic gas of massive galaxy clusters. The universal temperature profile in cool-core clusters and the theoretical mass–temperature relation suggest that the maximum effect of sedimentation must take place in the most massive virialized objects in the Universe. However, observational data from the Chandra and XMM-Newton observatories demonstrate more complex scaling relations between the masses of early-type galaxies and other parameters, such as the mass fraction and temperature of the interstellar gas. An important fact is that the radial temperature profile can have both falling and rising patterns. We have calculated the diffusion based on the observed gas density and temperature distributions for 13 early-type galaxies that have different envelope types and cover a wide range of X-ray luminosities. To estimate the maximum effect of sedimentation and thermal diffusion, we have solved the full set of Burgers equations for a non-magnetized interstellar plasma. The results obtained demonstrate a considerable increase of the He/H ratio within one effective radius for all galaxies of our sample. For galaxies with a falling or constant temperature profile the average increase of the helium abundance is 60% in one billion years of diffusion. The revealed effect can introduce a significant bias into the metal abundance estimate based on X-ray spectroscopy and can affect the evolution of stars that could be formed from a gas with a high helium abundance.     

Revised recommended methods for analyzing crater size-frequency distributions

Impact crater populations help us to understand solar system dynamics, planetary surface histories, and surface modification processes. A single previous effort to standardize how crater data are displayed in graphs, tables, and archives was in a 1978 NASA report by the Crater Analysis Techniques Working Group, published in 1979 in Icarus. The report had a significant lasting effect, but later decades brought major advances in statistical and computer sciences while the crater field has remained fairly stagnant. In this new work, we revisit the fundamental techniques for displaying and analyzing crater population data and demonstrate better statistical methods that can be used. Specifically, we address (1) how crater size-frequency distributions (SFDs) are constructed, (2) how error bars are assigned to SFDs, and (3) how SFDs are fit to power-laws and other models. We show how the new methods yield results similar to those of previous techniques in that the SFDs have familiar shapes but better account for multiple sources of uncertainty. We also recommend graphic, display, and archiving methods that reflect computers’ capabilities and fulfill NASA's current requirements for Data Management Plans.     

Region of motion in the Sitnikov four-body problem when the fourth mass is finite

This article deals with the region of motion in the Sitnikov four-body problem where three bodies (called primaries) of equal masses fixed at the vertices of an equilateral triangle. Fourth mass which is finite confined to moves only along a line perpendicular to the instantaneous plane of the motions of the primaries. Contrary to the Sitnikov problem with one massless body the primaries are moving in non-Keplerian orbits about their centre of mass. It is investigated that for very small range of energy h the motion is possible only in small region of phase space. Condition of bounded motions has been derived. We have explored the structure of phase space with the help of properly chosen surfaces of section. Poincarè surfaces of section for the energy range ?0.480≤h≤?0.345 have been computed. We have chosen the plane (q ₁,p ₁) as surface of section, with q ₁ is the distance of a primary from the centre of mass. We plot the respective points when the fourth body crosses the plane q ₂=0. For low energy the central fixed point is stable but for higher value of energy splits in to an unstable and two stable fixed points. The central unstable fixed point once again splits for higher energy into a stable and three unstable fixed points. It is found that at h=?0.345 the whole phase space is filled with chaotic orbits.     

Achromatic interfero-coronagraph with variable rotation shearing for studying extrasolar planets

Direct observation of exoplanets will make it possible to clarify many principal questions connected both with extrasolar planets and planetary systems and to measure atmospheric spectra of the planets. Obtaining an exoplanet image not distorted by the light from a star is at the cutting edge of present-day optical technologies owing to the combination of tremendous brightness contrasts and small angular distances between the planet and star. To observe the exo-Earth, it is necessary to weaken the brightness of the parent star image by 9–10 orders of magnitude (in the optical and near-IR ranges). To compensate the influence of the atmosphere, ground-based (e.g., 8–10 m) telescopes intended for observing exoplanets are equipped with adaptive optics systems, the spatial and temporal resolutions of which are not yet sufficient. A meter-class space telescope equipped with a star coronagraph will make it possible to observe the nearest exoplanets. In this paper, an improved tool for star coronagraphy is considered, namely, the achromatic interferometric coronagraph with a variable rotational shear. It is fabricated according to the optical scheme of the common path interferometer for studying extrasolar planets by direct observations. Theoretical and experimental estimations for the main characteristics of the scheme were carried out. Laboratory experimental measurements were carried out on a coronagraph model.     

Modelling the X-ray cluster dipole and cluster contribution to the soft X-ray background

We investigate the sampling and dipole convergence properties of flux-limited samples of mock X-ray clusters in relation to their underlying 'parent' cluster distribution. To this purpose, we resort to numerical simulations of the cluster distribution and extract samples resembling the main observational features of X-ray selected cluster samples. The flux-limited samples, being quite sparse, underestimate the amplitude of the 'parent' cluster dipole by ≈ 15 per cent on average for Local Group-like observers. However, the general shapes of their dipole amplitude profiles are in relatively good agreement. We also calculate the expected contribution of clusters, selected according to the relevant criteria, to the soft (i.e. 0.1–2.4 keV) extragalactic X-ray background (XRB), using the ESO Key Project X-ray luminosity function, assuming a flat universe with vanishing cosmological constant. We obtain a value of about 10 per cent of the observed XRB flux.     

The Deutsch field gamma-ray pulsar – II. Application of the model

A new model for gamma-ray pulsars presented by Higgins & Henriksen is applied to the cases of the seven known gamma-ray pulsars. Those pulsars that are not presently observed in gamma-rays, but are candidates for observation by the next generation of gamma-ray telescopes, are discussed. The case of millisecond pulsars is discussed, and it is shown that these objects should radiate at detectable levels, in opposition to the predictions of other gamma-ray pulsar models.