The chronology of a large ice-dammed lake and the Barents–Kara Ice Sheet advances, Northern Russia

Beach and shoreface sediments deposited in the more than 800-km long ice-dammed Lake Komi in northern European Russia have been investigated and dated. The lake flooded the lowland areas between the Barents–Kara Ice Sheet in the north and the continental drainage divide in the south. Shoreline facies have been dated by 18 optical stimulated luminescence (OSL) dates, most of which are closely grouped in the range 80–100 ka, with a mean of 88±3 ka. This implies that that the Barents–Kara Ice Sheet had its Late Pleistocene maximum extension during the Early Weichselian, probably in the cold interval (Rederstall) between the Brørup and Odderade interstadials of western Europe, correlated with marine isotope stage 5b. This is in strong contrast to the Scandinavian and North American ice sheets, which had their maxima in isotope stage 2, about 20 ka. Field and air photo interpretations suggest that Lake Komi was dammed by the ice advance, which formed the Harbei–Harmon–Sopkay Moraines. These has earlier been correlated with the Markhida moraine across the Pechora River Valley and its western extension. However, OSL dates on fluvial sediments below the Markhida moraine have yielded ages as young as 60 ka. This suggests that the Russian mainland was inundated by two major ice sheet advances from the Barents–Kara seas after the last interglacial: one during the Early Weichselian (about 90 ka) that dammed Lake Komi and one during the Middle Weichselian (about 60 ka). Normal fluvial drainage prevailed during the Late Weichselian, when the ice front was located offshore.     

Gamma ray astronomy beyond 2001: What instruments for the newt challenges?

In spite of the recent successes of SIGMA, RXTE andCompton GRO, and the launch of INTEGRAL in 2001, a lot ofquestions will stay opened for the next decades in gamma-ray astronomy.In this context we have to think about future instrument concepts whichwill allow a new step in the understanding of high-energy phenomena atwork in many exciting objects: binary systems with compact objects,active galactic nuclei, supernovae and novae, gamma ray bursters...A short overview of these new types of instruments will be given.     

A Chandra detection of the radio hotspot of 3C 123

Chandra X-ray Observatory observations of the powerful, peculiar radio galaxy 3C 123 have resulted in an X-ray detection of the bright eastern hotspot, with a 1-keV flux density of ∼5 nJy. The X-ray flux and spectrum of the hotspot are consistent with the X-rays being inverse-Compton scattering of radio synchrotron photons by the population of electrons responsible for the radio emission ('synchrotron self-Compton emission') if the magnetic fields in the hotspot are close to their equipartition values. 3C 123 is thus the third radio galaxy to show X-ray emission from a hotspot which is consistent with being in equipartition. Chandra also detects emission from a moderately rich cluster surrounding 3C 123, with L _X(2–10 keV)=2×10⁴⁴ erg s⁻¹ and kT ∼5 keV, and absorbed emission from the active nucleus, with an inferred intrinsic column density of 1.7×10²² cm⁻² and an intrinsic 2–10 keV luminosity of 10⁴⁴ erg s⁻¹.     

Evolution of the luminosity function and colours of galaxies in a Λ cold dark matter universe

The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Λ cold dark matter universe with the aid of a stellar population synthesis model. At     , the resulting B -band luminosity function has a flat faint-end slope of     with the characteristic luminosity and the normalization in fair agreement with observations, while the dark matter halo mass function is steep with a slope of     . The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from     to 5. A large evolution of the characteristic mass in the stellar mass function as a result of number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from     to 2, and then declines towards higher redshift, while the B -band luminosity density continues to increase from     to 5 (but only slowly at     .     

ISO Observations of Isolated Herbig AE/BE Stars

We report on SWS and LWS observations of the circumstellar disks of young stars of a few solar masses. The ISO spectra of these objects present a diversity of emission features of carbon-rich and oxygen-rich grains. The similarity of the forsterite spectra observed for Comet Hale-Bopp and the Haebe star HD100546 is particularly striking and provides a new argument that huge comet swarms are formed in the disks surrounding young stars. While the data suggest that the formation of crystalline silicates in the dust disks essentially occurs when a Haebe star has already reached the main sequence, no clear correlation with stellar age only is apparent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Variable Star Research With International Networks

Generally speaking, variable stars are monitored through observing campaigns which coordinate multi-site telescopes at various longitudes. A new practice is in progress: devoted networks involving robotic telescopes. We will review these two technologies and will emphasize the NORT (Network of Oriental Robotic Telescopes) project which we are promoting in North Africa, Middle-Eastern countries and Asia. This revised version was published online in July 2006 with corrections to the Cover Date.     

Surface Photometry of Comet Hale-Bopp Carbon Images

A very long series of photographic observations of the comet Hale-Bopp has been made during January–April 1997 at the double astrograph (400/2000) of the Main Astronomical Observatory (Kyiv, Ukraine). Some of the cometary photos were obtained with two wide-band filter combinations. One of these combinations isolates C₂ emission, another — the nearby dust continuum. The images were digitized by means of AMDPH-XY machine and then calibrated following the standard procedure. After subtraction of the dust continuum the distribution of surface brightness in the C₂ emission coma of comet Hale-Bopp was studied. We found an asymmetric brightness distribution both pre- and post-perihelion. On 21.77 April 1997 a secondary brightness peak is found at the distance of 1.03 × 10⁵ km from the nucleus. It is possible that this peak is related to the extended source of the C₂ molecules. This revised version was published online in July 2006 with corrections to the Cover Date.     

Main stages of evolution of matter in the universe. I

The problem of the equation of state of cosmic matter is discussed and the constants of integration in the Friedmann solutions are determined. Translated from Astrofizika, Vol. 40, No. 1, pp. 117–124, January–March, 1997.     

Terminal Outflow Velocities from the Mass-Losing AGB Stars

We have calculated terminal gas outflow velocities from the circumstellar shells of the AGB stars. Our results confirm that, in case of the stationary dust driven winds, the dynamics of the outflow is governed essentially by the dust properties and stellar luminosities, while only marginally by other stellar parameters. Although being far from comprehensive, our calculations also indicate that the dust driven winds may only occur in cool, luminous, low mass objects. This revised version was published online in September 2006 with corrections to the Cover Date.     

Small angle neutron scattering by opals

Micro- and non-crystalline opals, chalcedony and flint show diffuse small angle neutron scattering (SANS). Precious opals give rise to two additional intensity maxima at very small scattering angles which are due to Bragg reflections from the closest packed non-crystalline silica spheres. A small angle texture diagram reveals that the closest packing is faulty. Synthetic non-crystalline opals yield much less intense small angle scattering due to lower contrast between silica spheres and interstitial cement or particles; in this case intensity maxima were not observed. The outer part of the scattering curves of opal-CT and microcrystalline quartz deviates from Porod's law. The specific surface of natural non-crystalline opals ranges from 0.006 to 0.018 nm^–1. In microcrystalline opals, the specific surface is about 10 times larger than in non-crystalline opals.