A speckle interferometry survey of lambda Bootis stars

A search for duplicity of X Boo stars has been made by using the speckle ca mera installed at the Telescopio Nazionale Galileo. The operation mode and the reduction procedure allow one to obtain not only the separation, but al so the magnitude difference between the components; the latter parameter is fundamental for determining the degree of contamination from the secondary component of a binary system and thus the importance of the veiling effect that produces: absorption lines weaker than normal. Two stars, HD 38545 an d HD 290492. are close binaries with values of the separation and of tl-le magnitude difference such that only a composite spectrum can be observed. F or another 15 lambda Boo candidates, observed with negative results, the up per limits of a possible companion separation are given.