Non-LTE abundance analysis of A-B stars with low rotational velocities – II. Do A-B stars with normal abundances exist?

Abstract

ABSTRACT We present chemical composition and fundamental parameters (the effective temperature, surface gravity, and radius) for four sharp-lined A-type stars γ Gem (HD 41705), o Peg (HD 214994), θ Vir (HD 114330), and ν Cap (HD 193432). Our analysis is based on a self-consistent model fitting of high-resolution spectra and spectrophotometric observations over a wide wavelength range. We refined the fundamental parameters of the stars with the sme (Spectroscopy Made Easy) package and verified their accuracy by comparing with the spectral energy distribution and hydrogen line profiles. We found Teff/log g = 9190 ± 130 K/3.56 ± 0.08, 9600 ± 50 K/3.81 ± 0.04, 9600 ± 140 K/3.61 ± 0.12, and 10200 ± 220 K/3.88 ± 0.08 for γ Gem, o Peg, θ Vir, and ν Cap, respectively. Our detailed abundance analysis employs a hybrid technique for spectrum synthesis based on classical model atmospheres calculated in local thermodynamic equilibrium (LTE) assumption together with the non-LTE (NLTE) line formation for 18 of 26 investigated species. Comparison of the abundance patterns observed in A stars of different types (normal A, Am, and Ap) with similar fundamental parameters reveals significant abundance diversity that cannot be explained by the current mechanisms of abundance peculiarity formation in stellar atmospheres. We found a rise of the heavy element (Zn, Sr, Y, Zr, and Ba) abundance excess up to +1 dex with Teff increasing from 7200 to 10 000 K, with a further decrease down to solar value at Teff = 13 000 K, indicating that stars with solar element abundances can be found among late B-type stars.