A purely geometric distance to the binary star Atlas, a member of the Pleiades

We present radial velocity and new interferometric measurements of the double star Atlas, which permit, with the addition of published interferometric data, to precisely derive the orbital parameters of the binary system and the masses of the components. The derived semi-major axis, compared with its measured angular size, allows to determine a distance to Atlas of 132± 4 pc in a purely geometrical way. Under the assumption that the location of Atlas is representative of the average distance of the cluster, we confirm the distance value generally obtained through main sequence fitting, in contradiction with the early Hipparcos result (118.3± 3.5 pc).

Based on observations made with the ELODIE echelle spectrograph mounted on the 1.93-m telescope at the Observatoire de Haute-Provence (CNRS), with the FEROS echelle spectrograph mounted on the 2.2-m telescope at ESO-La Silla Observatory (programme No. 072.D-0235B), with the CORALIE echelle spectrograph mounted on the 1.2-m Euler Swiss telescope at ESO-La Silla Observatory, with the Naval Prototype Optical Interferometer (US Naval Observatory) and with the Mark III stellar interferometer at Mt Wilson.