Abundance Analysis of Planetary Host Stars. I. Differential Iron Abundances

We present atmospheric parameters and iron abundances derived from high-resolution spectra for three samples of dwarf stars: stars that are known to host close-in giant planets (CGP), stars for which radial velocity data exclude the presence of a close-in giant planetary companion (no-CGP), as well as a random sample of dwarfs with a spectral type and magnitude distribution similar to that of the planetary host stars (control). All stars have been observed with the same instrument and have been analyzed using the same model atmospheres, atomic data, and equivalent width modeling program. Abundances have been derived differentially to the Sun, using a solar spectrum obtained with Callisto as the reflector with the same instrumentation. We find that the iron abundances of CGP dwarfs are on average 0.22 dex greater than that of no-CGP dwarfs. The iron abundance distributions of both the CGP and no-CGP dwarfs are different than that of the control dwarfs, while the combined iron abundances have a distribution that is very similar to that of the control dwarfs. All four samples (CGP, no-CGP, combined, and control) have different effective temperature distributions. We show that metal enrichment occurs only for CGP dwarfs with temperatures just below solar and ≈300 K higher than solar, whereas the abundance difference is insignificant at Teff around 6000 K.