Search Publications
A secondary clump of red giant stars: why and where
Girardi, Léo
Based on the results of detailed population synthesis models, Girardi et al. recently claimed that the clump of red giants in the colour-magnitude diagram (CMD) of composite stellar populations should present an extension to lower luminosities, which goes down to about 0.4mag below the main clump. This feature is made of stars just massive enough …
The domain of γ Doradus variables in the Hertzsprung-Russell diagram
Handler, G.
70 new γ Doradus candidates were identified from Hipparcos photometry, which represents more than a doubling of the presently known number. Selecting the objects with good evidence for multiperiodicity, it is found that these stars, together with bona fide members of the class, occupy a well-defined region in a colour-magnitude diagram. This domai…
Velocity distribution of stars in the solar neighbourhood
Cottrell, P. L.; Hearnshaw, J. B.; Skuljan, J.
A two-dimensional velocity distribution in the UV plane has been obtained for stars in the solar neighbourhood, using Hipparcos astrometry for over 4000 `survey' stars with parallaxes greater than 10mas and radial velocities found in the Hipparcos Input Catalogue. In addition to the already known grouping characteristics (field stars plus young mo…
Structure and colour-magnitude diagrams of Scorpius OB2 based on kinematic modelling of Hipparcos data
de Bruijne, Jos H. J.
All stars in a `moving group' share the same space motion. The presence of such a coherent structure in velocity space can be used to derive (improved) estimates of the stellar parallaxes from the observed positions and proper motions. A Lund Observatory group (Dravins et al.) describes an elegant and sophisticated maximum likelihood procedure to …
Deriving star formation histories: inverting Hertzsprung-Russell diagrams through a variational calculus maximum likelihood method
Gilmore, Gerard; Valls-Gabaud, David; Hernandez, X.
We introduce a new method for solving maximum likelihood problems through variational calculus, and apply it to the case of recovering an unknown star formation history, SFR(t), from the resulting Hertzsprung-Russell (HR) diagram. This approach allows a totally non-parametric solution, which has the advantage of requiring no initial assumptions ab…
A refurbished convergent-point method for finding moving groups in the HIPPARCOS Catalogue
de Bruijne, Jos H. J.
The Hipparcos data allow a major step forward in the research of `moving groups' in the Solar neighbourhood, as the common motion of group members causes converging proper motions. Previous knowledge of these coherent structures in velocity space has always been limited by the availability, reliability and accuracy of ground-based proper-motion me…
Homogeneous photometry and metal abundances for a large sample of Hipparcos metal-poor stars*
Clementini, G.; Sneden, C.; Carretta, E. +1 more
Homogeneous photometric data (Johnson V, B-V, V-K, Cousins V-I and Strömgren b-y), radial velocities, and abundances of Fe, O, Mg, Si, Ca, Ti, Cr and Ni are presented for 99 stars with high-precision parallaxes measured by the Hipparcos satellite. These data have been previously used to assist the derivation of accurate distances and ages of Galac…
High-resolution spectroscopy of ROSAT-discovered weak-line T Tauri stars near Lupus
Hauschildt, P. H.; Alcalá, J. M.; Covino, E. +3 more
We present high-resolution optical echelle spectroscopy for a large fraction of the Li-rich late-type stars recently discovered in the vicinity of the Lupus dark clouds. Our results confirm the high Liilambda6708 equivalent widths previously estimated from medium-resolution spectra, thus adding strength to the conclusion that the large majority of…
Identification of moving groups and member selection using HIPPARCOS data
Aguilar, Luis A.; Hoogerwerf, Ronnie
A new method to identify coherent structures in velocity space - moving groups - in astrometric catalogues is presented: the Spaghetti method. It relies on positions, parallaxes and proper motions, and is ideally suited to searching for moving groups in the Hipparcos Catalogue. No radial-velocity information is required. The method has been tested…
Direct calibration of the Cepheid period-luminosity relation
Paturel, G.; Garnier, R.; Lanoix, P.
After the first release of Hipparcos data, Feast & Catchpole gave a new value for the zero-point of the visual Cepheid period-luminosity relation, based on trigonometric parallaxes. Because of the large uncertainties on these parallaxes, the way in which individual measurements are weighted is of crucial importance. We therefore conclude that …