Towards the solution of the lambda Bootis problem

Having analysed the accretion-based model of the dust-gas separation, which is regarded to be the most promising for the explanation of the anomalous properties of lambda Bootis-type stars, we can conclude that: (i) for any r easonable density profiles of the shell, dust grains appear to be decoupled from the gaseous background within the region where the temperature drops to a value that is less than the condensation temperature of heavy elements such as Mg, Ca, Fe, etc; (ii) most likely, in the shell of lambda Bootis-t ype stars only small dust particles (of less than approximate to 10(-6) cm in size) can be created; (iii) significant alteration of the initial atmosp heric chemical composition can take place in the case when the density in t he shell changes as similar to r(-2).