Abundance anomalies in the CP star HD 22920

Abstract

Using spectroscopic material of 16.9 Å/mm of dispersion, atmospheric parameters and chemical abundances of the CP star HD 22920 are determined. This star has been classified as a B8p Si - λ4200 by some authors while other included it the He- weak group. The atmospheric parameters, Teff=14500 K, log g=3.3 are determined from a "Kiel diagram", obtained from the comparison between observational and theoretical indices of the UBV and uvbyβ photometry and of the profiles of the Balmer lines. With these parameters and the ATLAS 6 program a model atmospheres is generated. Theoretical line profiles are computed using BALMER 6 code, a reasonable agreement with the observed ones is found. Microturbulent velocity is estimated from TiII, FeII and ZrII lines by requiring the abundances to be independent of equivalent widths. The value obtained is ζ = 2.5 km s⁻¹. Helium abundance is estimated from the comparison between observed and theoretical line profiles, it is less than the solar value by a factor of 10. Metallic abundances are calculated with the WIDTH 6 program; it is found that Mg, Si, S and Fe are normal; C, N and O are slightly overabundant while P, Ti, Cr, Mn, Sr, Y, Zr, Pt and Rare Earths are greatly overabundant. These results compared with the prediction of the diffusion theory. HD 22920 belongs definitely to the CP4 group of the CP stars, namely, to the He- weak stars.