The Geneva-Copenhagen survey of the solar neighbourhood^*

III. Improved distances, ages, and kinematics

¹ The Niels Bohr Institute, Astronomy Group, Juliane Maries Vej 30, 2100 Copenhagen, Denmark e-mail: [birgitta;johan]@astro.ku.dk
² Nordic Optical Telescope Scientific Association, Apartado 474, 38700 Santa Cruz de La Palma, Spain

Received: 20 October 2008
Accepted: 19 December 2008

Abstract

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 the largest available sample with complete data for stars with ages spanning that of the disk.

Aims. We aim to improve the accuracy of the GCS data by implementing the recent revision of the Hipparcos parallaxes.

Methods. The new parallaxes yield improved astrometric distances for 12 506 stars in the GCS. We also use the parallaxes to verify the distance calibration for uvbyβ photometry by Holmberg et al. (2007, A&A, 475, 519; GCS II). We add new selection criteria to exclude evolved cool stars giving unreliable results and derive distances for 3580 stars with large parallax errors or not observed by Hipparcos. We also check the GCS II scales of T_eff and [Fe/H] and find no need for change.

Results. Introducing the new distances, we recompute M_V for 16 086 stars, and U, V, W, and Galactic orbital parameters for the 13 520 stars that also have radial-velocity measurements. We also recompute stellar ages from the Padova stellar evolution models used in GCS I-II, using the new values of M_V, and compare them with ages from the Yale-Yonsei and Victoria-Regina models. Finally, we compare the observed age-velocity relation in W with three simulated disk heating scenarios to show the potential of the data.

Conclusions. With these revisions, the basic data for the GCS stars should now be as reliable as is possible with existing techniques. Further improvement must await consolidation of the T_eff scale from angular diameters and fluxes, and the Gaia trigonometric parallaxes. We discuss the conditions for improving computed stellar ages from new input data, and for distinguishing different disk heating scenarios from data sets of the size and precision of the GCS.