Lithium on the surface of cool magnetic CP stars I. Summary of spectroscopic observations with three telescopes

We present new results of observations of the 6708 Å line in twelve CP stars made with three telescopes: the ESO CAT the Crimean Observatory (CrAO) 2.6-m telescope, and the Nordic Optical Telescope (NOT). Unique profile and wavelength variations of the line at 6708 Å were discovered in two stars, HD 60435 and HD 83368. We present arguments in favour of the identification of this feature with the resonant Li i line. According to the incidence and variability of this line, spectra of twelve stars were divided in four groups: Group I - the line is remarkably variable in intensity and wavelength: this group includes the stars HD 83386 and HD 60435; Group 2 - the line is variable to a lesser extent; includes θ CrB and HD 188041; Group 3 - the line is not variable; includes 33 Lib. HD 134214, HD 166473 and γ Equ; Group 4 - the line is not present; includes HD 42659, HD 80316, HD 118022 and HD 128898. The behaviour in Groups 1-3 can be explained by the existence of Li rich spots on the star's surface using the oblique rotator model with different inclination and magnetic obliquity for each star. For HD 83368 we have found a light correlation between the visibility of the spots and the orientation of the dipole pulsation mode.