Evidence for the nearby F4V star λ Ara as a binary system

Abstract

We report on the spectroscopic evidence for the nearby, bright and supposedly single F4V star λ Ara as a binary system. The basic observational tracer is a discrepancy with the Hipparcos-based astrometric surface gravity as opposed to the spectroscopically derived value from the pressure-dependent Mg Ib triplet lines. We demonstrate how this discrepancy can be met with an equal-mass secondary hidden in the light of the star’s considerable projected rotational velocity vsin i = 15.5 ± 1.0 km s^-1 and we expect this scenario to be testable with high-angular resolution direct imaging observations. A major consequence should be the discovery of other nearby binary systems with a similar architecture.