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We present the first spatially resolved study of molecular gas in the vicinity of a gamma-ray burst (GRB), using CO(2-1) emission-line observations with the Atacama Large Millimetre Array at ∼50 pc scales. The host galaxy of GRB 980425 contains a ring of high column density H i gas, which is likely to have formed due to a collision between the GRB host and its companion galaxy, within which the GR
The ESA space astrometry mission Gaia will measure the positions, parallaxes and proper motions of the 1 billion brightest stars on the sky. Expected accuracies are in the 725 as range down to 15 mag and sub-mas accuracies at the faint limit (20 mag). The astrometric data are complemented by low-resolution spectrophotometric data in the 3301000 nm wavelength range and, for the brighter stars, radi
Observationally, the galactic chemical evolution of sulphur shows a complex pattern. Some studies find no correlation between [S/Fe] and [Fe/H] at halo metallcities, which is typical for alpha -elements, others find [S/Fe] increasing towards lower metallicities, and still others find a combination of the two. Each scenario has different implications for the Galactic chemical evolution of sulphur.
The influence of strong, large-scale magnetic fields on the structure and temperature distribution in white dwarf atmospheres is investigated. Magnetic fields may provide an additional component of pressure support, thus possibly inflating the atmosphere compared to the non-magnetic case. Since the magnetic forces are not isotropic, atmospheric properties may significantly deviate from spherical s
We show that the Galactic thick disk reaches at least solar metallicities and that it experienced strong chemical enrichment during a period of ~3 Gyr, ending around 8-9 Gyr ago. This finding puts further constraints on the relation and interface between the thin and thick disks and their formation processes. Our results are based on a detailed elemental abundance analysis of 261 kinematically sel
Photoinduced Ba L x-rays were measured, in the excitation energy range of 5.6-30 keV, by using high-brilliance undulator radiation. The obtained intensity ratios, the excitation-energy independent L beta(4)/L beta(3), L eta/L beta(1), L iota/L alpha(1,2), L beta(6)/ L alpha(1,2) and L beta(2,15)/L alpha(1,2) as well as the excitation- energy dependent L beta(1)/L alpha(1,2), L beta(3)/L alpha(1,2)
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We consider possible schemes for the resonance-enhanced two-photon ionization (RETPI) of Ne and Ar atoms under the action of bichromatic radiation of intense resonance lines of HI, HeI, and HeII in a radiation-rich astrophysical plasma. The ionization rate is comparable to or exceeds the recombination rate in rarified astrophysical plasma, which leads to the accumulation of singly ionized ions wit
Previously, weak emission lines had been detected at red wavelengths inthe spectra of a limited sample of mid to late B type main sequencestars. A fuller description of the occurrence and origins of these lineshas yet to be forwarded, in part due to the lack of observationsdetailing the spectral transitions involved. To address this deficiency,we present a line list of weak emission features found
Both the Fe II UV emission in the 2000-3000 Å region [Fe II(UV)]and resonance emission line complex of Mg II at 2800 Å areprominent features in quasar spectra. The observed Fe II(UV)/Mg IIemission ratios have been proposed as means to measure the buildup ofthe Fe abundance relative to that of the alpha-elements C, N, O, Ne,and Mg as a function of redshift. The current observed ratios show largesca
Using a numerical simulation of compressible convection with radiativetransfer mimicking the solar photosphere, we compare the velocity fieldderived from granule motions to the actual velocity field of the plasma.We thus test the idea that granules may be used to trace large-scalevelocity fields at the sun's surface. Our results show that this isindeed the case provided the scale separation is suf
P-mode oscillations in the Sun and stars are excited stochasticly by Reynolds stress and entropy fluctuations produced by convection in their outer envelopes. The excitation increases with increasing effective temperature (until envelope convection ceases in the F stars) and also increases with decreasing gravity.
The enrichment of Fe relative to α-elements such as O and Mgrepresents a potential means to determine the age of quasars and probethe galaxy formation epoch. To explore how Fe II emission in quasars islinked to physical conditions and abundance, we have constructed an 830level Fe II model atom and investigated through photoionizationcalculations how Fe II emission strengths depend on nonabundancef
We present numerical simulations that reproduce the salient features of the amazingly strong [Fe ii andFe ii emission spectra in the B and D Weigelt blobs of Carinae. For our studies we have used spectraobtained during the 1998 epoch observations with the Hubble Space Telescope (HST). The spectrum of the Band D Weigelt blobs dominates in [Fe ii and Fe ii emission lines. The same observations show
We report a strong prepulse dependence of the emission of X-rays from plasmas created by 150 fs Ti:sapphire laser pulses on solids. The laser pulses were focused onto plane samples of aluminium and vanadium with a main pulse power density of about 2.5 x 10(16) W cm(-2). By splitting off a portion of the main pulse we were able to generate a prepulse whose delay and intensity were variable relative
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our∼63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipp
New, precise abundance data for a large number of elements in a growingsample of extremely metal-poor stars are accumulating from the new 8-mtelescopes. Combined with theoretical models, these results advance ourunderstanding of the first generations of stars, whose nucleosynthesisproducts are fossilised in the oldest stars we see today and thus giveclues to the earliest phases of evolution in the
A method is presented for estimating the long exposure point spreadfunction (PSF) degradation due to tilt anisoplanatism in alaser-guide-star-based multiconjugate adaptive optics systems fromcontrol loop data. The algorithm is tested in numerical Monte Carlosimulations of the separately driven low-order null-mode system, and isshown to be robust and accurate with less than 10 relative error inboth
