HD 210111: a new λ Bootis-type spectroscopic binary system

Abstract

The small group of λ Bootis stars comprises late B- to early F-type stars, with moderate to extreme (up to a factor of 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O and S). The main mechanisms responsible for this phenomenon are atmospheric diffusion, meridional mixing and accretion of material from their surroundings. In particular, spectroscopic binary (SB) systems with λ Bootis-type components are very important to investigate the evolutionary status and accretion process in more detail. For HD 210111, δ Scuti-type pulsation was also found, which gives the opportunity to use the tools of asteroseismology for further investigations. The latter could result in strict constraints for the amount of diffusion for this star. Together with models for the accretion and its source, this provides a unique opportunity to shed more light on these important processes. We present classification and high-resolution spectra for HD 210111. A detailed investigation of the most likely combinations of single star components was performed. For this, composite spectra with different stellar astrophysical parameters were calculated and compared to the observations to find the best-fitting combination. HD 210111 comprises two equal (within the estimated errors) stars with Teff= 7400 K, log g= 3.8 dex, [M/H] =-1.0 dex and v sin i= 30 km s-1. This result is in line with other strict observational facts published so far for this object. This is only the third detailed investigation of the λ Bootis-type SB system, but the first one with a known infrared excess.