Elemental abundance trends in the Galactic thin and thick disks as traced by nearby F and G dwarf stars

Abstract

Abstract. Based on spectra from F and G dwarf stars, we present elemental abundance trends in the Galactic thin and thick disks in the metallicity regime −0.8 [Fe/H] +0.4. Our findings can be summarized as follows. 1) Both the thin and the thick disks show smooth and distinct abundance trends that, at sub-solar metallicities, are clearly separated. 2) For the α-elements the thick disk shows signatures of chemical enrichment from SNe type Ia.3) The age of the thick disk sample is in the mean older than the thin disk sample. 4) Kinematically, there exist thick disk stars with super-solar metallicities. Based on these findings, together with other constraints from the literature, we discuss different formation scenarios for the thick disk. We suggest that the currently most likely formation scenario is a violent merger event or a close encounter with a companion galaxy. Based on kinematics the stellar sample was selected to contain stars with high probabilities of belonging either to the thin or to the thick Galactic disk. The total number of stars are 66 of which 21 belong to the thick disk and 45 to the thin disk. The analysis is based on high-resolution spectra with high signal-to-noise (R ∼ 48 000 and S /N 150, respectively) recorded with the FEROS spectrograph on La Silla, Chile. Abundances have been determined for four α-elements (Mg, Si, Ca, and Ti), for four even-nuclei iron peak elements (Cr, Fe, Ni, and Zn), and for the light elements Na and Al, from equivalent width measurements of ∼30 000 spectral lines. An extensive investigation of the atomic parameters, log g f -values in particular, have been performed in order to achieve abundances that are trustworthy. Noteworthy is that we find for Ti good agreement between the abundances from Ti  and Ti . Our solar Ti abundances are in concordance with the standard meteoritic Ti abundance.

Spectroscopic stellar parameters for 582 FGK stars in the HARPS volume-limited sample

“…This is useful to access the consistency between the various methods that use either spectroscopy or photometry to derive stellar parameters. We used the spectroscopic results of Edvardsson et al (1993), Bensby et al (2003), and , and the photometric results of Nordström et al (2004) and Casagrande et al (2011). Figure 4 compares our measurements of the effective temperature (panel (a)) and [Fe/H] (panel (b)) with those of Nordström et al (2004), which used the calibrations of Alonso et al (1996) to derive the effective temperatures.…”

The GAPS programme with HARPS-N at TNG

“…This is because the thin disk and the thick disk within the Milky Way are discrete populations showing distinct chemical distributions in several elements, and in particular in α-elements. In fact, the Galactic thin and thick disks appear to overlap significantly around −0.7 < ∼ [Fe/H] < ∼ 0.0 dex when the iron abundance is used as a reference, while they are separated in [α/Fe] (see, e.g., Bensby et al 2003;Mishenina et al 2004). Here, we investigate to which population the XO-2 stellar system belongs to take advantage of 431 stars listed in the catalog by Soubiran & Girard (2005) and 906 FGK dwarf stars analyzed by Adibekyan et al (2012) with thin-disk, thick-disk, and halo membership probabilities (P thin , P thick , P halo ) higher than 90%.…”

Stellar Populations of the Galactic Disk: Metallicity Distribution and Kinematics

“…Such stars are often selected for kinematical study by their metallicity ([Fe/H] in the range -0.5 and -1 dex) or for chemical study by their kinematics (rotational lag behind the LSR taken to be 20-60 km s −1 and larger). However, there is strong evidence for both the extremely metal-week tail to [Fe/H] below -1.6 dex (Beers et al 2002) and the high-metallicity tail extending to super-solar values (Bensby et al 2003) in the distribution of the thick-disk field stars, which indicates that [Fe/H] is less discriminant than velocities to separate this population.…”