Vertical distribution of Galactic disk stars

IV. AMR and AVR from clump giants

¹ Université Bordeaux 1, CNRS, Laboratoire d'Astrophysique de Bordeaux, BP 89, 33270 Floirac, France e-mail: soubiran@obs.u-bordeaux1.fr
² Université de Strasbourg, CNRS Observatoire Astronomique, 11 rue de l'Université, 67000 Strasbourg, France
³ Astronomical Observatory of Odessa National University, Shevchenko Park, 65014 Odessa, Ukraine

Received: 4 October 2007
Accepted: 30 November 2007

Abstract

We present the parameters of 891 stars, mostly clump giants, including atmospheric parameters, distances, absolute magnitudes, spatial velocities, galactic orbits and ages. One part of this sample consists of local giants, within 100 pc, with atmospheric parameters either estimated from our spectroscopic observations at high resolution and high signal-to-noise ratio, or retrieved from the literature. The other part of the sample includes 523 distant stars, spanning distances up to 1 kpc in the direction of the North Galactic Pole, for which we have estimated atmospheric parameters from high resolution but low signal-to-noise Echelle spectra. This new sample is kinematically unbiased, with well-defined boundaries in magnitude and colours. We revisit the basic properties of the Galactic thin disk as traced by clump giants. We find the metallicity distribution to be different from that of dwarfs, with fewer metal-rich stars. We find evidence for a vertical metallicity gradient of –0.31 dex kpc^-1 and for a transition at ~4–5 Gyr in both the metallicity and velocities. The age–metallicity relation (AMR), which exhibits a very low dispersion, increases smoothly from 10 to 4 Gyr, with a steeper increase for younger stars. The age–velocity relation (AVR) is characterized by the saturation of the V and W dispersions at 5 Gyr, and continuous heating in U.