Abundances of iron-peak elements in disk and bulge giant stars from high-resolution optical spectra

Abstract: Context. The formation and evolution of the Galactic bulge and the Milky Way is still a debated subject. Observations of, e.g., the X-shaped bulge, cylindrical stellar motions and young stars in the bulge have suggested that the bulge formed through secular evolution of the disk and not through gas dissipation and/or mergers, as thought previously.\\ Data. We use high-resolution optical spectra of 291 K giants in the local disk obtained by the FIES spectrograph on the Nordic Optical Telescope (S/N = 80-100 for most of the disk spectra) and 46 K giants in the bulge obtained by the UVES/FLAMES spectrograph on the ESO Very Large Telescope (S/N = 10-80). \\ Aims. The goal of this work is to examine stellar samples from the thin and thick disk as well as the bulge and measure abundances of six iron-peak elements (Sc, V, Cr, Mn, Co and Ni). These can provide additional observational constraints for Galaxy formation and chemical evolution models and help to understand whether the bulge has emerged from the (thick) disk or not. \\ Methods. We determine the abundances in the Solar neighbourhood and bulge by synthesising line profiles using the programme Spectroscopy Made Easy (SME) and 1-D, spherically-symmetric MARCS model atmospheres under the assumption of local thermodynamic equilibrium (LTE). We also separate the thin and thick disk stellar populations according to their [Ti/Fe]-ratios and radial velocities using a Gaussian Mixture Model (GMM). Moreover, we apply NLTE corrections for Co as well.\\ Results. The [(Sc,V,Co)/Fe] vs. [Fe/H] trends show a clear separation between the disk components, being more enhanced in the thick disk. The same is observed for Ni but to a lesser extent. The trends of Sc, V and Co are also more enhanced in the bulge compared to the thick disk, whereas the [Ni/Fe] ratio is similar in the thick disk and the bulge. Our [Mn/Fe] ratio steadily increases with increasing metallicity at about the same rate in all the three components. For Cr, we find a flat trend around [Cr/Fe] $\sim$0 for the whole metallicity range in the disk and the bulge. We also observe a higher average metallicity in the bulge compared to the disk.\\ Conclusions. The significantly enhanced [(Sc,V,Co)/Fe] ratios that we determine from our data of stars in the bulge, suggest that the local thick disk and the bulge have experienced different chemical enrichment and evolutionary paths. %This could depend on a faster chemical enrichment in the bulge than in the thick disk due to, e.g., a faster star formation rate. However, we are unable to predict the exact evolutionary path of the bulge solely based on these observations. Galactic chemical evolution models could, on the other hand, provide that using these results.