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We present a detailed chemical analysis of 22 stars along thecolour-magnitude sequence of the intermediate-age (1.7 Gyr) open clusterIC 4651, based on high-resolution, high S/N ratio spectra from UVES/VLT.IC 4651 thus becomes one of the few open clusters for which a detailedcomposition analysis exists for stars spanning 3.5 mag, from solar-typemain-sequence stars to giants above the RGB clump. In
Modelling the formation of super-km-sized planetesimals by gravitational collapse of regions overdense in small particles requires numerical algorithms capable of handling simultaneously hydrodynamics, particle dynamics and particle collisions. While the initial phases of radial contraction are dictated by drag forces and gravity, particle collisions become gradually more significant as filaments
Recent numerical simulations have shown long-lived axisymmetric sub- and super-Keplerian flows in protoplanetary disks. These zonal flows are found in local as well as global simulations of disks unstable to the magnetorotational instability. This paper covers our study of the strength and lifetime of zonal flows and the resulting long-lived gas over- and underdensities as functions of the azimuth
This paper presents a technique for reconstructing two interfering wavefronts by analyzing their 3D interference field pattern. The method is based on the numerical inverse problem and will present a robust algorithm for reconstructing of wavefronts. Several simulations are done to validate the proposed method. (C)2011 Optical Society of America
We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor and Large Area Telescope (LAT) instruments on board the Fermi Gamma-ray Space Telescope. GRB 090926A shares several features with other bright LAT bursts. In particular, it clearly shows a short spike in the light curve that is present in all detectors that see the burst, and this in turn
Context. Knowledge of the abundance distribution of star forming regions and young clusters is critical to investigate a variety of issues, from triggered star formation and chemical enrichment by nearby supernova explosions to the ability to form planetary systems. In spite of this, detailed abundance studies are currently available for relatively few regions. Aims. In this context, we present th
Aims. We seek to provide 2MASS and OGLE identifications and coordinates for all stars in the finding chart published by Arp (1965, ApJ, 141, 43). This chart covers the low extinction area around NGC 6522, also known as Baade's window, at coordinates (l, b) = (1.02, -3.92). Methods. A cross correlation, using numerical techniques, was performed between a scan of the original finding chart from Arp
The weighted oscillator strengths (gf) and lifetimes for S VIII presented in this work were obtained by a multiconfigurational Hartree-Fock relativistic approach. In this calculation, the electrostatic energy parameters were optimized by a least-squares procedure in order to improve the adjustment to experimental energy levels. The values for gf and lifetimes were then calculated on the basis of t
Aims. The aim of our new laboratory measurements is to measure accurate absolute oscillator strengths for neutral manganese transitions in the infrared needed for the study of late-type stars and ultracool dwarfs. Methods. Branching fractions have been measured by high resolution Fourier transform spectroscopy and combined with radiative level lifetimes in the literature to yield oscillator streng
In this paper we investigate the performance of a Fourier based algorithm for fast subpixel shift determination of two mutually shifted images subjected to noise. The algorithm will be used for Shack-Hartmann based adaptive optics correction of images of an extended object subjected to dynamical atmospheric fluctuations. The performance of the algorithm is investigated both analytically and by Mon
Using high-resolution spectra of nearby F and G dwarf stars, we have investigated the detailed abundance and age structure of the Hercules stream. We find that the stars in the stream have a wide range of stellar ages, metallicities, and element abundances. By comparing to existing samples of stars in the solar neighborhood with kinematics typical of the Galactic thin and thick disks, we find that
We present oxygen abundances for 72 F and G dwarf stars in the solarneighbourhood. Using the kinematics of the stars we divide them into twosub-samples with space velocities that are typical for the thick andthin disks, respectively. The metallicities of the stars range from[Fe/H] ≈ -0.9 to +0.4 and we use the derived oxygen abundances of thestars to: (1) perform a differential study of the oxygen
We discuss resonance-enhanced two-photon ionization (RETPI) and presentschemes of successive RETPI of the elements C, N, and O in nebulae.RETPI is activated by intrinsic radiation stored in the form of trappedspectral lines of HI, HeI, and HeII in the optically thick nebula. Therate of this two-step photoionization is comparable with or exceeds thelow recombination rate of the photoions formed in
Spectral lines observed in the Sr-filament of eta Car in the wavelengthregion 2480-10140{AA}. The lines are sorted by wavelength in table 2 andsorted according to the periodic table in table 3. Both tables areavailable in postscript format as the file tables23.ps where the sub andsuperscripts for the atomic transitions are kept.(2 data files).
Context. Extremely metal-poor (EMP) stars preserve a fossil record of the composition of the ISM when the Galaxy formed. It is crucial, however, to verify whether internal mixing has modified their surface composition, especially in the giants where most elements can be studied. Aims. We aim to understand the CNO abundance variations found in some, but not all EMP field giants analysed earlier. Mi
After the discovery of space masers based on OH radicals (Weaver et al.cite{Wea65}) and H2O (Cheung et al. cite{Che69}) such microwavelasers have been found to work in more than 100 molecular species(Elitzur cite{Eli92}; Townes cite{Tow97}), as well as in highlyexcited H atoms (Strelnitski et al. cite{Str96}). In the IR region (10mum), the effect of stimulated emission of radiation in t
About a hundred dust impacts per day were detected during the first week in December 1995 by Galileo during its approach to Jupiter. These impacts were caused by submicrometer-sized particles that were just above the detection limit. After the closest approach to Io on 7 December, impacts of these small particles ceased. This effect is expected for dust grains emitted from Io that exit the field o
Three-dimensional numerical simulations with CO5, a newradiation hydrodynamics code, result in a dynamic, thermally bifurcatedmodel of the non-magnetic chromosphere of the quiet Sun. The 3D modelincludes the middle and low chromosphere, the photosphere, and the topof the convection zone, where acoustic waves are excited by convectivemotions. While the waves propagate upwards, they steep
Analyses of their internal stellar kinematics imply that the dwarf spheroidal (dSph) companion galaxies to the Milky Way are among the most dark matter-dominated systems known. Should there be significant dark matter in the form of faint stars in these systems, the stellar luminosity function must be very different from that of a similar metallicity globular cluster, for which there is no evidence
