Abundances in HD27411 and the helium problem in Am stars

TL;DR

This study analyzes the chemical abundances in the star HD27411, compares atmospheric modeling techniques, and investigates the helium problem in Am stars, revealing insights into their temperature, luminosity, and pulsation characteristics.

Contribution

It demonstrates that ATLAS9 is sufficient for moderate chemical peculiarities and provides new insights into the helium deficiency issue in Am stars.

Findings

ATLAS9 and ATLAS12 yield similar abundance results.

Effective temperatures from Stromgren photometry are reliable.

No significant helium depletion in the pulsation driving zone.

Abstract

We analyze a high-resolution spectrum of the A3m star HD27411. 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 Stromgren indices derived from calculated spectra with the atmospheric abundances of HD27411. We find that the effective temperatures of Am/Fm stars derived from Stromgren 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 delta Scuti stars shows quite clearly that there is no significant decrease of helium in the driving zone, contrary to current models of diffusion.