Chemical gradients in the Milky Way from the RAVE data

II. Giant stars

¹ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
e-mail: corrado@ari.uni-heidelberg.de
² Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, 67000 Strasbourg, France
³ Leibniz Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁴ Rudolf Peierls Centre for Theoretical Physics, Keble Road, Oxford OX1 3NP, UK
⁵ Sydney Institute for Astronomy, School of Physics A28, University of Sydney, Sydney NSW 2006, Australia
⁶ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁷ Research School of Astronomy and Astrophysics, Australian National University, Cotter Rd., ACT 2611 Weston, Australia
⁸ Institute for Computational Astrophysics, Dept of Astronomy and Physics, Saint Mary’s University, Halifax, NS, BH3 3C3, Canada
⁹ Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE, UK
¹⁰ INAF Osservatorio Astronomico di Padova, via dell’Osservatorio 8, 36012 Asiago, Italy
¹¹ Department of Physics and Astronomy, Padova University, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
¹² Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P5C2, Canada
¹³ Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109, Australia
¹⁴ Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670, Australia
¹⁵ Research Centre for Astronomy, Astrophysics and Astrophotonics, Macquarie University, Sydney, NSW 2109, Australia
¹⁶ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT, UK
¹⁷ Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
¹⁸ Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia

Received: 10 April 2014
Accepted: 20 June 2014

Abstract

Aims. We provide new constraints on the chemo-dynamical models of the Milky Way by measuring the radial and vertical chemical gradients for the elements Mg, Al, Si, Ti, and Fe in the Galactic disc and the gradient variations as a function of the distance from the Galactic plane (Z).

Methods. We selected a sample of giant stars from the RAVE database using the gravity criterium 1.7 <log g< 2.8. We created a RAVE mock sample with the Galaxia code based on the Besançon model and selected a corresponding mock sample to compare the model with the observed data. We measured the radial gradients and the vertical gradients as a function of the distance from the Galactic plane Z to study their variation across the Galactic disc.

Results. The RAVE sample exhibits a negative radial gradient of d[Fe/H]/dR = −0.054 dex kpc^-1 close to the Galactic plane (| Z | < 0.4 kpc) that becomes flatter for larger | Z |. Other elements follow the same trend although with some variations from element to element. The mock sample has radial gradients in fair agreement with the observed data. The variation of the gradients with Z shows that the Fe radial gradient of the RAVE sample has little change in the range | Z | ≲ 0.6 kpc and then flattens. The iron vertical gradient of the RAVE sample is slightly negative close to the Galactic plane and steepens with | Z |. The mock sample exhibits an iron vertical gradient that is always steeper than the RAVE sample. The mock sample also shows an excess of metal-poor stars in the [Fe/H] distributions with respect to the observed data. These discrepancies can be reduced by decreasing the number of thick disc stars and increasing their average metallicity in the Besançon model.