From near-infrared, narrow-band photometry of 256 oxygen-rich Mira variables we obtain evidence about the loops that these stars follow in colour-colour diagrams. We also find a phase lag between indices related to molecular band-strength of titanium oxid
With the HST PC and uvby photometry, we investigate evolutionary signatures in a field in the centre of the LMC Bar. Field stars close to the turn off point in the HR diagram are used for a study of ages and evolution of the stellar popu lations dominatin
Recently 3D hydrodynamical simulations of stellar surface convection have become feasible thanks to advances in computer technology and efficient numerical algorithms. Available observational diagnostics indicate that these models are highly realistic in describing the topology of stellar granulation and for spectral line formation purposes. The traditional free parameters (mixing length parameters, micro- and macroturbulence) always inherent in standard 1D analyses have thus finally become obsolete. These 3D models can therefore both shed light on the elusive nature of stellar convection as well as be employed in element abundance analyses. In the present contribution we will describe some aspects of the models and possible applications of them in terms of radiative transfer.
We have constructed line-blanketed model atmospheres for the hydrogen-deficient and carbon-rich R Coronae Borealis (RCrB) stars, as well as for the similar hydrogen-deficient carbon (HdC) stars and the cool extreme helium (EHe) stars. Improved continuum o
The surface chemical composition of this remarkable star shows that it is hydrogen-deficient, carbon-rich and enriched in the light s-process elements. Spectra taken in May and October 1996 indicate a decrease in the surface hydrogen abundance by 0.7 dex
The elemental abundances of the mildly hydrogen-deficient R Coronae Borealis (R CrB) star V854 Cen have been estimated. The R CrB stars have been divided into majority and minority classes judging by their abundance patterns. Class assignment has previous
The available data on M class asteroids have been collected and analysed. The possible number of M-asteroids in the main asteroid belt larger than 30 km was estimated to be about 90 objects. A list of the 60 asteroids currently classified as M is presente
We present broadband images, two-colour maps and spectra of a magnitude limited sample of interacting and merging galaxies.
In our search for nearby young and unevolved galaxies we encountered ESO 146 - G14, a blue low-surface-brightness late-type disc galaxy with remarkable properties. The analysis of the chemical abundances of the brightest Hn regions yields an oxygen abunda
We present luminosity profiles, colour profiles and disk parameters based on near-infrared JHK surface photometry of a sample of blue low surface brightness galaxies (BLSBGs). The results are discussed along with previously obtained optical data. We find
In an effort to detect the early phases of star formation in massive galaxies, we have searched for Ly alpha and [O II]lambda 3727 emission from four QSO metal absorption line systems and possible associated galaxies, using narrow-band filters. None of th
Broad band colors and bolometric corrections in the Johnson-Cousins-Glass system (Bessell, 1990; Bessell & Brett, 1988) have been computed from synthetic spectra from new model atmospheres of Kurucz (1995a), Castelli (1997), Plez, Brett & Nordlund (1992),
Ultraviolet spectra obtained with the Hubble Space Telescope of the carbon star TX Piscium (HR 9004) are presented, along with analysis providing information on its outer atmosphere, including flow and turbulent velocities, line formation mechanisms, and
We investigate the main differences between static 1D and 3D time-dependent model stellar atmospheres of red giants at very low metallicities. We focus in particular on the impact of 3D LTE spectral line formation on the derivation of elemental abundances for the extremely metal-poor ([Fe/H] ≈-5.3) red giant HE 0107-5240.
We investigate the impact of realistic three-dimensional (3D) hydrodynamical model stellar atmospheres on the determination of elemental abundances in the carbon-rich, hyper-iron-poor stars HE 0107-5240 and HE 1327-2326. We derive the chemical compositions of the two stars by means of a detailed 3D analysis of spectral lines under the assumption of local thermodynamic equilibrium (LTE). The lower temperatures of the line-forming regions of the hydrodynamical models cause changes in the predicted spectral line strengths. In particular, we find the 3D abundances of C, N, and O to be lower by about -0.8 dex (or more) than estimated from a 1D analysis. The 3D abundances of iron peak elements are also decreased but by smaller factors (about -0.2 dex). We caution, however, that the neglected non-LTE effects might actually be substantial for these metals. We finally discuss possible implications for studies of early Galactic chemical evolution.
The collision velocities and collision frequencies of Hilda asteroids have been investigated numerically. The collision probabilities and collision velocities have been determined from a data base of close encounters, obtained by numerical integrations of
Reflectance spectra with a wavelength coverage between 4000-9100 Angstrom have been obtained for eight Hilda asteroids with the 2.2m telescope at the European Southern Observatory in Chile. From the obtained spectra we determined the Tholen taxonomy for f
We obtained 49 reflectance spectra of 23 Hilda asteroids in the wavelength ranges 3850-7650 and 3850-10150 Angstrom during two observing runs in 1992. The primitive D-types dominate and comprise 34% of the numbered Hilda asteroids, while 28% and 2% are P
The lightcurves of 47 Hilda asteroids presented in Dahlgren et al, (1998, Icarus 133, 247-285) have been analyzed. The Hilda population has mean lightcurve amplitudes significantly larger than those of main-belt asteroids of similar sizes, This is due to
The results of a photometric survey of Hilda asteroids are presented. We have obtained 224 lightcurves of 47 Hilda asteroids. A wide span of rotation periods have been found, ranging from 2.851 to 31 h. However, indications of rotation periods longer than
We discuss the determination of carbon isotopic ratios C-12/C-13 in N-type Galactic carbon stars. Ohnaka & Tsuji (1996) reported C-12/C-13 ratios Smaller by a factor 2 or 3 than the determinations of Lambert et al. (1986). Using synthetic spectra of carbo
de Laverny & Gustafsson (1998, Paper 1) questioned the iso-intensity method used by Ohnaka & Tsuji (1996) to derive carbon isotopic ratios in cool carbon stars. As a reply Ohnaka & Tsuji (1998) pointed out that the method criticized in Paper I differs fro
The results of photometric observations of 9 asteroids collected from 1991 to 1997 are presented. The observations have been conducted at Belogradchik and Rozhen observatories, Bulgaria. For 42 Isis a spin pole determination has been performed: we derive
We have determined chemical abundances and radial velocities for stars in the field of the zeta Sculptoris cluster. We find that the cluster metal deficiency previously found from UBV photometry is not supported; the cluster overall metallicity, [Fe/H] =
The asteroid 85 Io has been observed using CCD and photoelectric photometry on 18 nights during its 1995-96 and 1997 apparitions. We present the observed lightcurves, determined colour indices and modelling of the asteroid spin vector and shape. The colou
We have derived elemental abundances of O, Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Co, Ni as well as for a number of s-elements for 47 G and K dwarf, with [Me/H]> 0.1 dex. The selection of stars was based on their kinematics as well as on their uvby - beta ph
We have observed the B I lambda 2497 line to derive the boron abundances of two very metal-poor stars selected to help in tracing the origin and evolution of this element in the early Galaxy: BD +23 degrees 3130 and HD 84937. The observations were conduct
We present non-LTE corrections to abundances of Fe, O, Na, and Mg derived from LTE analyses of F-K stars over a broad range of gravities and metal abundances; they were obtained using statistical equilibrium calculations and new model atoms. Line opacity
Developments in the modelling of stellar atmospheres and results from the confrontation between calculated and observed fluxes and spectra are discussed. It is argued that, although impressive advances in the study of O-type, WR and cool star spectra have
The impact of high-precision astrometry on modelling of stellar spectra and determination of fundamental stellar parameters for single stars is discussed. It is found to be considerable, but improvements in the understanding of stellar atmospheres, and in
Various observable properties of the Sun are compared with those of solar-type stars. It is concluded that the Sun, to a remarkable degree, is "solar-type". As regards its particular mass and age, and probably its non-binarity, "anthropic" explanations ma
The effects of molecules on model stellar atmospheres are briefly reviewed. Molecular diagnostics of stellar fundamental parameters and of atmospheric structure are discussed, and the presently emerging "ISO picture" of the outer regions of stars is comme
Circumstellar envelopes around three bright N-type stars, R Scl, X TrA, and V Aql have been detected in emission in resonance lines from K I. This radiation, which is most probably scattered photospheric radiation, was first found spectroscopically, but h