On the Binarity of Carbon-Enhanced, Metal-Poor Stars

TL;DR

This study investigates the binarity of carbon-enhanced, metal-poor stars by monitoring their radial velocities, revealing that all CEMP-s stars in the sample are in binary systems, supporting the mass transfer hypothesis.

Contribution

It provides the first comprehensive radial velocity monitoring of CEMP stars, confirming the binary nature of CEMP-s stars and linking them to AGB mass transfer processes.

Findings

44% of CEMP-s stars are in binary systems

All CEMP-s stars in the sample are binaries

Supports the mass transfer origin of CEMP-s star peculiarities

Abstract

We report on a programme to monitor the radial velocities of a sample of candidate and confirmed carbon-enhanced, metal-poor (CEMP) stars. We observed 45 targets using the Echelle Spectrographs of three 4m class telescopes. Radial velocities for these objects were calculated by cross-correlation of their spectra with the spectrum of HD 140283, and have errors < 1 km/s. Sixteen of our programme's targets have reported carbon excess, and nine of these objects also exhibit s-process enhancements (CEMP-s). We combine these stars' radial velocities with other literature studies in search of binarity. The search reveals that four of our CEMP-s stars (44%) are in binary systems. Using the analysis of Lucatello et al. (2004), we find that all the CEMP-s stars in our sample are binaries. This conclusion implies that CEMP-s stars may be the very metal-poor relatives of CH and Ba II stars, which are believed to have acquired their peculiar abundance patterns by mass transfer from a thermally-pulsing AGB companion.