The Chemical Compositions of Galactic Disk F and G Dwarfs

Abstract

Photospheric abundances are presented for 27 elements from carbon to europium in 181 F-G dwarfs from a differential LTE analysis of high-resolution and high signal-to-noise spectra. Stellar $T_{\mathrm{eff}}$ were adopted from an infrared flux method calibration of Strömgren photometry. Stellar log $g$ were calculated from {\it Hipparcos} parallaxes and stellar evolutionary tracks. Stellar space motions ($U,V,W$) and a Galactic potential were used to estimate Galactic orbital parameters. Results of $\alpha$-elements -- O, Mg, Si, Ca, and Ti -- show [$\alpha$/Fe] to increase slightly with decreasing [Fe/H]. Heavy elements with dominant contributions at solar metallicity from the $s$-process show [$s$/Fe] to decrease slightly with decreasing [Fe/H]. Scatter in [X/Fe] at a fixed [Fe/H] is entirely attributable to the small measurement errors, after excluding the few thick disc stars and the $s$-process enriched CH subgiants. Tight limits are set on `cosmic' scatter. By combining our sample with published studies, thick disc stars are identified by their $V_{LSR}$ in the range $-40$ to -100 km s${}^{-1}$. These are very old stars with origins in the inner Galaxy and metallicities [Fe/H] $\le -0.4$. At the same [Fe/H], the sampled thin disc stars have $V_{LSR}\sim 0$ km s${}^{-1}$, and are generally younger with a birthplace at about the Sun's Galactocentric distance. In the range $-$0.35 $\ge$ [Fe/H] $\ge$ $-$0.70, well represented by present thin and thick disc samples, [X/Fe] of the thick disc stars is greater than that of thin disc stars for Mg, Al, Si, Ca, Ti, and Eu. [X/Fe] is very similar for the thin and thick disc for -- notably -- Na, and iron-group elements.

51 pages (includes 19 figures and 6 tables). To appear in MNRAS (paper has been replaced: typos added, In Table~1, [Fe/H]phot has been replaced by spectroscopic [Fe/H] that are used in the plots) (Table1, photometric[Fe/H] values are replaced by spectroscopically derived [Fe/H] that are used in the plots)