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The stellar initial mass function at high redshift is an important defining property of the first stellar systems to form and may also play a role in various dark matter problems. We here determine the faint stellar luminosity function in an apparently dark-matter-dominated external galaxy in which the stars formed at high redshift. The Ursa Minor dwarf spheroidal galaxy is a system with a particu

We consider the conditions necessary for the development of an inverted population among the energy levels of free atoms in a medium exposed to radiation in spectral non- equilibrium. In particular, we focus on monochromatic radiation occurring as a result of an accidental wavelength coincidence between a pumping emission line and a pumped absorption line in two different elements. We examine espe

We present a review of some of the current major challenges in stellar cluster research, including young clusters, globular clusters, and galactic nuclei. Topics considered include: primordial mass segregation and runaway mergers, expulsion of gas from clusters, the production of stellar exotica seen in some clusters (e.g., blue stragglers and extreme horizontal-branch stars), binary populations w

We present a simple, semi--analytical description for the final stagesof mergers of black hole (BH) -- neutron star (NS) systems. Such systemsare of much interest as gravitational wave sources and gamma--ray burstprogenitors. Numerical studies show that in general the neutron star isnot disrupted at the first phase of mass transfer. Instead, what remainsof the neutron star is left on a wider, ecce

The most precise method of investigating possible space-time variations of the fine-structure constant, alpha equivalent to (1/hc)(e(2)/4 pi epsilon(0)), using high-redshift quasar absorption lines is the many-multiplet (MM) method. For reliable results this method requires very accurate relative laboratory wavelengths for a number of UV resonance transitions from several different ionic species.

The dust detector system onboard Galileo has recoding dust impacts incircumjovian space since the spacecraft was injected into a bound orbitabout Jupiter in December 1995. This is the sixth in a series of papersdedicated to presenting Galileo and Ulysses dust data. We present datafrom the Galileo dust instrument for the period January to December 1996when the spacecraft completed four orbits about

We study the nature of the peculiar [Sr II] and Sr II emission filament found in the ejecta of Eta Carinae. To this purpose we carry out abinitio calculations of radiative transition probabilities and electron impact excitation rate coefficients for Sr II. Then we build a multilevel model for the system which is used to investigate the physical condition of the filament and the nature of the obser

Recent progress on the nature of short-duration gamma-ray bursts has shown that a fraction of them originate in the local Universe. These systems may well be the result of giant flares from soft gamma-repeaters (highly magnetized neutron stars commonly known as magnetars). However, if these neutron stars are formed via the core collapse of massive stars then it would be expected that the bursts sh

A brief description of the operational principles of an Electron Beam Ion Trap is given with specific reference to the currently under development/construction Shanghai EBIT. This is followed by an introduction to some of the frontier physics problems of highly charged ions that can be studied with such devices. Also a discussion of the use of EBITs as a powerful tool in hot-plasma diagnostics is

We have modelled the formation of the eccentric double-degenerate binaries J1141-6545 and B2303+46 using the Henyey-type full stellar evolution code STARS and the population synthesis code BSE. We find that the outcome depends strongly on the common envelope (CE) evolution efficiency parameter alpha(CE) and show that both systems can be modelled with a single value of alpha(CE). The final orbit of

Two short (< 2 s) gamma-ray bursts (GRBs) have recently been localized(1-4) and fading afterglow counterparts detected(2-4). The combination of these two results left unclear the nature of the host galaxies of the bursts, because one was a star-forming dwarf, while the other was probably an elliptical galaxy. Here we report the X-ray localization of a short burst (GRB 050724) with unusual gamma-ra

We report on a new survey of metallicities, ages, and Galactic orbitsfor a complete, magnitude-limited, and kinematically unbiased all-skysample of 16682 nearby F- and G-dwarfs. Our~63000 new, accurate radialvelocities for nearly 13500 of the stars, combined with Hipparcosparallaxes and Tycho-2 proper motions, complete the kinematic data for14139 stars and allow us to identify most of the binary s

We propose that a radiative cycle operates in atoms and ions located ina rarefied gas in the vicinity of a hot star. Besides spontaneoustransitions the cycle includes a stimulated transition in one very weakintermediate channel. This radiative bottleneck creates apopulation inversion, which for an appropriate column density results inamplification and stimulated radiation in the weak transition. T

Identical in situ dust detectors are flown on board the Galileo and Ulysses spacecraft. They record impacts of micrometeoroids in the ecliptic plane at heliocentric distances from 0.7 to 5.4 AU and in a plane almost perpendicular to the ecliptic from -79 deg to +79 deg ecliptic latitude. The combination of both Ulysses and Galileo measurements yields information about the radial and latitudinal di

Giant planets form out of a disc of gas and dust – called protoplanetary disc -- that surrounded the protosun at the time of its formation. While the cores of giant planets were growing via planetesimal and pebble accretion, they started to interact with the gas in the protoplanetary disc. These interactions can lead to inward migration of all the four giant planets in our Solar System during the