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Pulsation models of δ Scuti variables. I. The high-amplitude double-mode stars.
Christensen-Dalsgaard, J.; Petersen, J. O.
The relations between high-amplitude δ Scuti stars and the much more abundant low-amplitude δ Sct variables are not clear. Both groups have similar periods and seem to have almost the same basic physical properties, although their light-curve characteristics are very different. In the last few years much improved observational data have been publi…
HIPPARCOS distances and mass limits for the planetary candidates: 47 Ursae Majoris, 70 Virginis, and 51 Pegasi
Evans, D. W.; Arenou, F.; Lindegren, L. +19 more
Distances to the recently-discovered planetary system candidates, 47 UMa, 70 Vir and 51 Peg, are presented, based on absolute trigonometric parallaxes from the global reduction of the ESA Hipparcos astrometry satellite data. Standard errors of the parallaxes are in the range 0.66-0.76mas (milliarcsec), with resulting distances accurate to around 1…
Searching for VIMs: an astrometric method to detect the binary nature of double stars with a variable component
Wielen, R.
The photo-center of a close double star in which one component has a variable luminosity moves on the sky in the same rhythm as the total luminosity of the system varies in time. This provides an astrometric method to detect the binary nature of the system if more direct methods fail. We propose to call such systems `variability-induced movers', o…
On the width of the theoretical lower main sequence. Consequences for the determination of the {DELTA}Y/{DELTA}Z ratio in the solar neighbourhood.
Baglin, A.; Lebreton, Y.; Fernandes, J.
We discuss the relation between the main sequence thickness and chemical composition variations. With the help of theoretical zero-age main sequence models between 0.7 and 1.0Msun_, computed with an advanced physical description of the stellar interiors, in a range of metallicities typical from Population I stars (0.008<=Z<=0.034)…
The empirical white dwarf mass-radius relation and its possible improvement by HIPPARCOS
Schmidt, H.
The famous mass-radius relation of white dwarf stars is based on theoretical considerations. The structure of a white dwarf, and thereby its fundamental properties, are deduced from the physical properties of the degenerate electron gas. Numerical computations take temperature and evolution effects into consideration. However, the few cases in whi…
Proper motion study of the globular cluster M 92.
Tucholke, H. -J.; Scholz, R. -D.; Brosche, P.
We present proper motions for stars in the field of the galactic globular cluster NGC6341 (M92). This study continues the series of papers from the Bonn programme of globular cluster proper motions. Plates taken with the Bonn double refractor and the Rozhen observatory 2m Ritchey-Chretien telescope with a maximal epoch difference of 94years were u…
Absolute magnitudes and kinematics of oxygen Mira variables.
Luri, X.; Figueras, F.; Torra, J. +1 more
A new maximum likelihood method, using apparent magnitudes, proper motions and radial velocities, has been applied to a sample of 90 Mira stars extracted from the HIPPARCOS Input Catalogue (INCA) to determine absolute magnitudes and kinematics. Using this new method three different groups of Mira stars have been identified in the sample, with diff…
The galactic warp in young stars proper motions.
Lattanzi, M. G.; Smart, R. L.
Using Monte Carlo simulations of the Galaxy parameters, we have investigated the expected effects of a galactic warp model on the proper motions of early type stars. The introduction of the warp into the Galaxy simulation appears very pronounced in galactic latitude proper motions, but unobservable in galactic longitude proper motions. The proper …
Comparison of the Carlsberg optical reference frame with the International Celestial Reference Frame.
Fabricius, C.; Jones, D. H. P.; Morrison, L. V. +4 more
The optical positions of 63 extragalactic nebulae measured in the frame defined by the annual series of Carlsberg Meridian Catalogues Nos 1-8 are compared with their VLBI radio positions in the International Celestial Reference Frame. The differences between these radio and optical positions are interpreted as showing the global distortion of the …
Relative astrometry with Hipparcos: double stars with orbital motion.
Badiali, M.; Cardini, D.; Emanuele, A. +2 more
During the Hipparcos data analysis an algorithm was developed to study orbital motion in double stars and to derive the seven Dommanget parameters in the positive cases. Three approaches were followed: linear motion model, quadratic motion model and orbital model. In the last model the algorithm needs sufficiently good starting values and it has b…