Parent Stars of Extrasolar Planets. VI. Abundance Analyses of 20 New Systems

The results of new spectroscopic analyses of 20 recently reported extrasolarplanet parent stars are presented. The companion of one of these stars, HD10697, has recently been shown to have a mass in the brown dwarf regime; wefind [Fe/H] $= +0.16$ for it. For the remaining sample, we derive [Fe/H]estimates ranging from -0.41 to $+0.37$, with an average value of $+0.18 \pm0.19$. If we add the 13 stars included in the previous papers of this seriesand 6 other stars with companions below the 11 M$_{\rm Jup}$ limit from therecent studies of Santos et al., we derive $<$[Fe/H]$> = +0.17 \pm 0.20$. Among the youngest stars with planets with F or G0 spectral types, [Fe/H] issystematically larger than young field stars of the same Galactocentricdistance by 0.15 to 0.20 dex. This confirms the recent finding of Laughlin thatthe most massive stars with planets are systematically more metal rich thanfield stars of the same mass. We interpret these trends as supporting ascenario in which these stars accreted high-Z material after their convectiveenvelopes shrunk to near their present masses. Correcting these young starmetallicities by 0.15 dex still does not fully account for the difference inmean metallicity between the field stars and the full parent stars sample. The stars with planets appear to have smaller [Na/Fe], [Mg/Fe], and [Al/Fe]values than field dwarfs of the same [Fe/H]. They do not appear to havesignificantly different values of [O/Fe], [Si/Fe], [Ca/Fe], or [Ti/Fe], though.Comment: 54 pages of text and tables; 12 figures; to be published in the Astronomical Journa