- (1) Heidelberg University, grid.7700.0
- (2) Aarhus University, grid.7048.b, AU
- (3) University of Copenhagen, grid.5254.6, KU
- (4) University of Notre Dame, grid.131063.6
- (5) Harvard-Smithsonian Center for Astrophysics, grid.455754.2
Context. The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20−70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon; these are the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems.