V474 Car: A Rare Halo RS CVn Binary in Retrograde Galactic Orbit

TL;DR

V474 Car is a rare, high-velocity halo RS CVn binary star with extreme eccentricity and retrograde orbit, showcasing unique stellar activity and orbital characteristics unlike typical pre-main sequence stars.

Contribution

This paper reports the discovery and detailed analysis of V474 Car as a rare halo RS CVn binary with retrograde orbit, high eccentricity, and extreme velocity, expanding understanding of such systems.

Findings

V474 Car is a metal-poor, tidally-locked binary star.

It has an extremely eccentric orbit with high velocity.

It is one of the few known halo RS CVn binaries.

Abstract

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 (10.3 days), enhanced Li, and absolute magnitude that places it above the main sequence. However, its extreme radial velocity (264 km s$^{-1}$) suggested that this system was unlike any previously known pre-MS system. Our detailed spectroscopic analysis of echelle spectra taken with the CTIO 4-m finds that V474 Car is both a spectroscopic binary with orbital period similar to the photometric rotation period, and metal poor ([Fe/H] $\simeq -$0.99). The star's Galactic orbit is extremely eccentric (e $\simeq$ 0.93) with perigalacticon of only $\sim$0.3 kpc of the Galactic center - and its eccentricity and smallness of its perigalacticon are only surpassed by $\sim$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 (CAB), i.e.\ a halo RS CVn binary, and one of only a few such specimens known.