1997A&A...319..637H

Result. from spectroscopic observations in the Li region of the binary CP star β CrB (HD 137909, HR 5747, F0p ) are presented. The observations were carried out at the Crimean Observatory from 1993 to 1995 with the coude spectrograph equipped with a CCD detector, R=45000. We have analyzed the 6693-6721Å region by means of the spectral synthesis method by assuming a model with parameters T_eff=8000K, logg=4.0, and [M/H]=1.0. We derived abundances for the elements with lines in the studied range. The observed feature at 6708Å is not well fitted by the Li doublet even by assuming an isotopic ratio 10 times the terrestrial value and an overabundance of lithium of 2.6dex; a very good fit is obtained assuming a blend with V I at 6708.094Å, in the hypothesis that Vanadium is in excess by a factor larger than 10³ (a value which is not confirmed by other abundance determinations). It is more probable that the Li feature is blended with some unidentified line due to some overabundant heavy element. The ultraviolet excess for λ<1600Å is discussed. It could be explained either by assuming that the companion is a λ Boo star having a metal deficiency [M/H]=-1.0 and T_eff∼8200K, or by assuming that β CrB is Si deficient, so that the Si I discontinuities at 1514.34Å and at 1674.03Å disappear. However, there is no clear evidence of underabundances of this element with respect to the solar value. The main results of this paper are: the variability of the lithium blend with the period of rotation of the star; the relations between rotational radial velocity, line intensity W_λ and FWHM variations for the Li blend and other lines of different elements - Fe Gd Ce - which show similar variations.