Non-interacting main-sequence binaries with different chemical compositions: Evidences of infall of rocky material?

We performed a careful differential abundance analysis of individual compon ents of six main sequence binaries with separations of a few hundreds of AU . To reduce analysis concerns, we selected systems with almost equal mass c omponents. We were able to derive differential abundances of several elemen ts with errors down to 0.01 dex in the best cases. We found that in four sy stems the two components have the same chemical composition, within these v ery severe limits. However, clear differences were found for the two remain ing systems (HD 219542 and HD 200466), in both cases the primaries being mo re Fe-rich than the secondaries, by 0.091 +/-0.009 and 0.053 +/-0.024 dex r espectively. Similar differences were found for most of the elements consid ered in our analysis; however, we found no appreciable difference for volat ile elements and a trend for increasing abundance differences with increasi ng condensation temperature for individual elements, a result similar to th at found for some single stars with planets by Smith et al. (2001). Finally , we note that HD 219542A has a Li-abundance comparable to those of Li-rich stars in old open clusters, while no Li is detected in the slightly cooler HD 219542B. We suggest that the primaries of these two systems have accret ed rocky planets or the inner dust-rich part of a protoplanetary disk, like ly due to gravitational perturbation caused by the presence of the companio n.