Search Publications
The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Holmberg, J.; Nordström, B.; Andersen, J.
Context: Ages, chemical compositions, velocity vectors, and Galactic orbits for stars in the solar neighbourhood are fundamental test data for models of Galactic evolution. The Geneva-Copenhagen Survey of the Solar Neighbourhood (Nordström et al. 2004; GCS), a magnitude-complete, kinematically unbiased sample of 16 682 nearby F and G dwarfs, is th…
The Peculiar Solar Composition and Its Possible Relation to Planet Formation
Gustafsson, B.; Yong, D.; Asplund, M. +1 more
We have conducted a differential elemental abundance analysis of unprecedented accuracy (~0.01 dex) of the Sun relative to 11 solar twins from the Hipparcos catalog and 10 solar analogs from planet searches. We find that the Sun shows a characteristic signature with a ≈20% depletion of refractory elements relative to the volatile elements in compa…
Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue
van Leeuwen, F.
Context: A new reduction of the astrometric data as produced by the Hipparcos mission has been published, claiming that the accuracies for nearly all stars brighter than magnitude Hp = 8 are improved, by up to a factor 4, compared to the original catalogue. As correlations between the underlying abscissa residuals have also been reduced by more th…
Kinematics and history of the solar neighbourhood revisited
Binney, James J.; Aumer, Michael
We use proper motions and parallaxes from the new reduction of Hipparcos data and Geneva-Copenhagen radial velocities for a complete sample of ~15000 main-sequence and subgiant stars, and new Padova isochrones to constrain the kinematics and star formation history of the solar neighbourhood. We rederive the solar motion and the structure of the lo…
The Extreme Microlensing Event OGLE-2007-BLG-224: Terrestrial Parallax Observation of a Thick-Disk Brown Dwarf
Lee, C. -U.; Fouque, P.; Bennett, D. P. +75 more
Parallax is the most fundamental technique for measuring distances to astronomical objects. Although terrestrial parallax was pioneered over 2000 years ago by Hipparchus (ca. 140 B.C.E.) to measure the distance to the Moon, the baseline of the Earth is so small that terrestrial parallax can generally only be applied to objects in the Solar System.…
Kinematics of OB-associations and the new reduction of the Hipparcos data
Dambis, A. K.; Mel'Nik, A. M.
The proper motions of OB-associations computed using the old and new reductions of the Hipparcos data are in good agreement with each other. The Galactic rotation curve derived from an analysis of the line-of-sight velocities and proper motions of OB-associations is almost flat in the 3-kpc neighbourhood of the Sun. The angular rotation velocity a…
Galactic Globular and Open Clusters in the Sloan Digital Sky Survey. II. Test of Theoretical Stellar Isochrones
Beers, Timothy C.; Masseron, Thomas; Pinsonneault, Marc H. +6 more
We perform an extensive test of theoretical stellar models for main-sequence (MS) stars in ugriz, using cluster fiducial sequences obtained in the previous paper of this series. We generate a set of isochrones using the Yale Rotating Evolutionary Code with updated input physics, and derive magnitudes and colors in ugriz from MARCS model atmosphere…
The interstellar Ca II distance scale
Krełowski, J.; Galazutdinov, G. A.; Strobel, A. +1 more
Aims: We attempt to extend the relation between the strengths of the interstellar Ca II lines and the distances to early-type stars to objects beyond 1 kiloparsec, with the line saturation taken into account.
Methods: We measure the Ca II K and Ca II H equivalent widths, and compute Ca II column densities for 262 lines of sight towards early-t…
Deep 2MASS Photometry of M67 and Calibration of the Main-Sequence J - KS Color Difference as an Age Indicator
Kirkpatrick, Allison; Dotter, Aaron; Sarajedini, Ata
We present an analysis of Two Micron All Sky Survey (2MASS) calibration photometry of the old open cluster M67 (NGC 2682). The proper-motion-cleaned color-magnitude diagram (CMD) resulting from these data extends ~3 mag deeper than one based on data from the point source catalog. The CMD extends from above the helium-burning red clump to a faint l…
Lithium abundances of halo dwarfs based on excitation temperature. I. Local thermodynamic equilibrium
García Pérez, A. E.; Norris, J. E.; Ryan, S. G. +2 more
Context: The discovery of the Spite plateau in the abundances of 7Li for metal-poor stars led to the determination of an observationally deduced primordial lithium abundance. However, after the success of the Wilkinson Microwave Anisotropy Probe (WMAP) in determining the baryon density, Ω_Bh2, there was a discrepancy between …