ABUNDANCE ANALYSIS OF THE LAMBDA-BOOTIS STARS HD-192640, HD-183324 AND HD-84123

The classification of lambda Bootis stars based on photometric indices or low resolution spectra is not sufficient for a final decision conc erning a membership to this group. A detailed spectroscopic investigat ion is necessary to rule out stars with similar classification spectra but different abundance patterns. Therefore a program on abundance an alyses of lambda Bootis candidates was established, which makes use of a software package that enables the analysis of high signal-to-noise spectra with large resolution. In this paper we present the results of the application of these tools on two lambda Bootis stars (HD 192640 and HD 183324), for which the derived abundances agree very well with the literature. For a third star (HD 84123), which shows a very low pr ojected rotational velocity, the newly determined abundance pattern co nfirms its membership to the lambda Bootis group. We also investigated the effect of using several different codes for the calculation of th e model atmospheres on the synthetic spectra of the program stars, whi ch span a wide range in effective temperature, gravity and metallicity . The substitution of opacity distribution functions, which where pret abulated for metal abundances scaled according to the solar compositio n, by ones calculated for the individual abundance patterns does not c hange the synthetic spectra significantly. On the other hand, the deri ved abundances are sensitive to the treatment of overshooting within t he calculation of the convective flux for cool stars.