Chemical abundances of 32 mildly metal-poor stars

Free access article

Issue		A&A Volume 449, Number 1, April I 2006


Page(s)		127 - 134
Section		Galactic structure, stellar clusters and populations
DOI		http://dx.doi.org/10.1051/0004-6361:20053770

A&A 449, 127-134 (2006)
DOI: 10.1051/0004-6361:20053770

Chemical abundances of 32 mildly metal-poor stars

H. W. Zhang¹ and G. Zhao²

¹ Department of Astronomy, School of Physics, Peking University, Beijing 100871, PR China
e-mail: zhw@bac.pku.edu.cn
² National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China

(Received 22 July 2005 / Accepted 26 October 2005 )

Abstract
Context.The formation scenario of the Galactic thick disk is an unresolved problem. Chemical abundances in long-lived dwarf stars of the thin and thick disks provide information of the Galactic disk formation.
Aims.We present photospheric abundances of the O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Ni, and Ba elements for 32 mildly metal-poor stars with ${\rm [Fe/H]}\sim -0.7$ . According to their kinematics, age, and [ $\alpha$ /Fe] , sample stars are identified to thin disk, thick disk, and halo population memberships. Element abundances for sample stars are discussed as a function of metallicity.
Methods.High resolution and high signal-to-noise ratio spectra were obtained with the Coudé Echelle Spectrograph mounted on the 2.16 m telescope at the National Astronomical Observatories (Xinglong, China). Effective temperatures were estimated from colour indices, and surface gravities from Hipparcos parallaxes. Stellar abundances were determined from a differential LTE analysis. The kinematics parameters were calculated from the parallax, proper motion, and radial velocity. Stellar ages were determined from theoretical stellar evolution tracks.
Results.The average age of the thick disk stars is older than the thin disk stars. Our element abundance results extend and confirm previous works. The oxygen and other $\alpha$ -elements (Mg, Si, Ca, and Ti) abundances of thin and thick disk stars show distinct trends at $\rm [Fe/H]\le-0.60$ . The [Al/Fe] behaviour is exactly as an $\alpha$ -element, although the separation for [Na/Fe] of thin and thick disk stars is not clear. The elements V, Cr, and Ni follow Fe very closely, and there is no offset between thin and thick disk stars, but the Sc and Mn abundance trends of the thin and thick disk stars are different, and [Ba/Fe] of thin disk and thick disk stars shows different behaviour.

Key words: stars: abundances -- stars: kinematics -- Galaxy: disk

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