V474 car: A rare halo RS CVn binary in retrograde Galactic orbit

We report the discovery that the star V474 Car is an extremely active, high velocity halo RS CVn system. The star was originally identified as a possible pre-main-sequence star in Carina, given its enhanced stellar activity, rapid rotation (10.3days), enhanced Li, and absolute magnitude which places it above the main sequence (MS). However, its extreme radial velocity (264kms ^-1) suggested that this system was unlike any previously known pre-MS system. Our detailed spectroscopic analysis of echelle spectra taken with the CTIO 4m finds that V474 Car is both a spectroscopic binary with an orbital period similar to the photometric rotation period and metal-poor ([Fe/H]≃-0.99). The star's Galactic orbit is extremely eccentric (e ≃ 0.93) with a perigalacticon of only 0.3kpc of the Galactic center - and the eccentricity and smallness of its perigalacticon are surpassed by only 0.05% of local F/G-type field stars. The observed characteristics are consistent with V474 Car being a high-velocity, metal-poor, tidally locked, chromospherically active binary, i.e., a halo RS CVn binary, and one of only a few such specimens known.