Astronomy and astrophysics vol:262 issue:2 pages:L37-L40
We propose that a low mass-accretion rate of gas and dust from a circumstellar or circum-system disc onto A-F type stars in very different evolutionary phases can lead to the selective accretion of only the gas due to the differential forces that act on the gas and the dust. This may result in a photosphere with a depletion pattern similar to that of the Interstellar Medium. Such a mechanism can explain the abundance patterns in lambda-Boo stars and in some post-AGB stars that are in wide binary systems. Accretion of clean gas from a circum-system disc in post-AGB binaries requires much less strict conditions on the binary evolution than the binary scenario proposed by Mathis & Lamers (1992) does.