Spectroscopic analysis of the SB3 system 74 Aqr

In this paper, we present the first quantitative abundance analysis of the SB3 system whose primary is the well-known mercury-manganese (HgMn) star 74Aqr (= HD 216494). From the fit of the Hβ profile, obtained at the orbital phase of maximum separation between A and B components, we determined the effective temperatures and surface gravities of each component: T eff A, = 12 000 K, log T eff A = 3.70, T eff B = 11 500 K, log g B = 3.90 and T eff C = 11 500 K, log g C = 4.10. These values are validated by the coincidence of abundances derived from different ionization states of iron. We find that this system is heterogeneous from the point of view of the chemical composition: HD 216494 A shows the typical spectral features, with the exception of strontium underabundance, of HgMn stars. Apart from a mild helium underabundance and overabundance of two rare earths (praseodymium and neodymium), HD 216494 B does not show any other anomaly. The fast rotating C component, in spite of the difficulties found in the identification of its spectral lines, seems to be the only normal star of the system.