Abundance differences between components of wide binaries

Abstract

In this paper we present iron abundance analysis for 23 wide binaries with main sequence components in the temperture range 4900-6300 K, taken from the sample of the pairs currently included in the radial velocity planet search on going at the TNG. The use of a line-by-line differential analysis technique between the components of each pair allows to reach errors of about 0.02 dex in the iron content difference. Most of the pairs have abundance differences lower than 0.02 dex and there are no pairs with differences larger than 0.07 dex. The four cases of differences larger than 0.02 dex may be spouriuos because of the larger error bars affecting pairs with large temperature difference, cold stars and rotating stars. The pair HD 219542, previously reported by us to have different composition, results instead normal. For non-rotating stars warmer than 5500 K, we are able to exclude in most cases the ingestion of more than 1 Earth Mass of iron (about 5 Earth masses of meteoritic material) during the main sequence lifetime of the stars, placing more stringent limits (about 0.4 Earth masses of iron) in five cases of warm stars. This latter limit is similar to the estimates of rocky material accreted by the Sun during its main sequence lifetime. Combining the results of the present analysis with those for the Hyades and Pleiades, we conclude that the hypothesis that pollution by planetary material is the only responsible for the highest metallicity of the stars with planets may be rejected at more than 99% level of confidence if the incidence of planets in these samples is as high as 8% and similar to the field stars included in current radial velocity surveys. However, the significance of this result drops considerably if the incidence of planets around stars in binary systems and clusters is less than a half than around normal field stars.