Abundances in HD 27411 and the helium problem in Am stars


E-mail: gca@oact.inaf.it


We analyse a high-resolution spectrum of the A3m star HD 27411. We compare abundances derived from atlas9 model atmospheres with those using the more computationally intensive atlas12 code. We found very little differences in the abundances, suggesting that atlas9 can be used for moderate chemical peculiarity. Our abundances agree well with the predictions of diffusion theory, though for some elements it was necessary to calculate line profiles in non-thermodynamic equilibrium to obtain agreement. We investigate the effective temperatures and luminosities of Am/Fm stars using synthetic Strömgren indices derived from calculated spectra with the atmospheric abundances of HD 27411. We find that the effective temperatures of Am/Fm stars derived from Strömgren photometry are reliable, but the luminosities are probably too low. Caution is required when deriving the reddening of these stars owing to line blanketing effects. A comparison of the relative proportions of pulsating and non-pulsating Am stars with δ Scuti stars shows quite clearly that there is no significant decrease of helium in the driving zone, contrary to current models of diffusion.