Search Publications
PPM-Extended (PPMX) - a catalogue of positions and proper motions
Schwan, H.; Scholz, R. -D.; Piskunov, A. E. +3 more
Aims: We build a catalogue PPM-Extended (PPMX) on the ICRS system which is complete down to a well-defined limiting magnitude and contains the best presently available proper motions suited for kinematic studies in the Galaxy.
Methods: We perform a rigorous weighted least-squares adjustment of individual observations, spread over more than a c…
Hipparcos distance estimates of the Ophiuchus and the Lupus cloud complexes
Alves, J.; Lombardi, M.; Lada, C. J.
We combine extinction maps from the Two Micron All Sky Survey (2MASS) with Hipparcos and Tycho parallaxes to obtain reliable and high-precision estimates of the distance to the Ophiuchus and Lupus dark complexes. Our analysis, based on a rigorous maximum-likelihood approach, shows that the ρ-Ophiuchi cloud is located at (119 ± 6) pc and the Lupus …
On the kinematic evolution of young local associations and the Scorpius-Centaurus complex
Figueras, F.; Torra, J.; Fernández, D.
Context: Over the last decade, several groups of young (mainly low-mass) stars have been discovered in the solar neighbourhood (closer than ~100 pc), thanks to cross-correlation between X-ray, optical spectroscopy and kinematic data. These young local associations - including an important fraction whose members are Hipparcos stars - offer insights…
Non-LTE line formation for heavy elements in four very metal-poor stars
Zhao, G.; Mashonkina, L.; Aoki, W. +6 more
Aims:Stellar parameters and abundances of Na, Mg, Al, K, Ca, Sr, Ba, and Eu are determined for four very metal-poor (VMP) stars (-2.15 ≥ [Fe/H] ≥ -2.66). For two of them, HD 84937 and HD 122563, the fraction of the odd isotopes of Ba derived for the first time.
Methods: Determination of an effective temperature, surface gravity, and element ab…
The red clump absolute magnitude based on revised Hipparcos parallaxes
Groenewegen, M. A. T.
Context: Over the past decade the use of the red clump (RC) as distance indicator has increased in importance as this evolutionary phase is well populated and a good local calibration exists.
Aims: The absolute calibration of the RC in the I and K band is investigated again based on the recently published revised Hipparcos parallaxes.
Meth…
Direct evidence of a sub-stellar companion around CT Chamaeleontis
Neuhäuser, R.; Schmidt, T. O. B.; Hauschildt, P. H. +5 more
Aims: In our ongoing search for close and faint companions around T Tauri stars in the Chamaeleon star-forming region, we here present observations of a new common proper motion companion to the young T-Tauri star and Chamaeleon member CT Cha and discuss its properties in comparison to other young, low-mass objects and to synthetic model spectra f…
Astrometric and photometric monitoring of GQ Lupi and its sub-stellar companion
Neuhäuser, R.; Schmidt, T. O. B.; Mugrauer, M. +2 more
Context: Neuhäuser et al. (2005, A&A, 435, L13) presented direct imaging evidence for a sub-stellar companion to the young T Tauri star GQ Lupi. Common proper motion was highly significant, but no orbital motion was detected. Faint luminosity, low gravity, and a late-M/early-L spectral type indicated that the companion is either a planet or a …
Young stars and brown dwarfs surrounding Alnilam (ɛ Orionis) and Mintaka (δ Orionis)
Caballero, J. A.; Solano, E.
Aims: We look for new regions to search for substellar objects.
Methods: Two circular areas, 45 arcmin-radius each, centred on the young massive star systems Alnilam and Mintaka in the Orion Belt, were explored. The regions are very young (less than 10 Ma), have low extinction, and are neighbours to σ Orionis (~3 Ma), a young open cluster very…
The long-period Galactic Cepheid RS Puppis. I. A geometric distance from its light echoes
Szabados, L.; Kervella, P.; Bersier, D. +4 more
Context: The bright southern Cepheid RS Pup is surrounded by a circumstellar nebula reflecting the light from the central star. The propagation of the light variations from the Cepheid inside the dusty nebula creates spectacular light echoes that can be observed up to large distances from the star itself. This phenomenon is currently unique in thi…
A probable close brown dwarf companion to GJ 1046 (M 2.5V)
Kürster, M.; Reffert, S.; Endl, M.
Context: Brown dwarf companions to stars at separations of a few AU or less are rare objects, and none have been found so far around early-type M dwarfs (M 0V-M 5V). With GJ 1046 (M 2.5V), a strong candidate for such a system with a separation of 0.42 AU is presented.
Aims: We aim at constraining the mass of the companion in order to decide wh…