1997A&A...320..257L

Even if metal and helium abundances characterize the stellar atmosphere structure, the effective temperature and gravity of stars are generally determined assuming the solar chemical composition. To investigate the importance of such a simplification, we have performed high resolution spectroscopy of the H_β region for the helium weak stars HD 5737, HD 175362 and HD 202671, which are also known to be metal rich. By spectral synthesis of the H_β line profile, the effective temperature and gravity of these stars have been inferred using atmosphere models whose metal opacity scale, metal and helium abundances were consistent with the derived abundances. It appears that the effective temperature and gravity are under-estimated if the metal and/or the helium abundance are under-estimated. For HD 175362 the richest in metal star of our sample, without taking into account the correct metal and helium abundance the effective temperature can be under-estimated up to 7% and the logarithm of gravity can be under-estimated up to 0.25dex.