The elusive origin of Carbon-Enhanced Metal-Poor stars

TL;DR

This paper investigates the origins of Carbon-Enhanced Metal-Poor stars by testing the impact of wind Roche-lobe overflow on their population, revealing increased CEMP fractions and different distribution patterns compared to traditional models.

Contribution

It introduces the use of wind Roche-lobe overflow in population synthesis models to better explain CEMP star characteristics, improving upon previous BHL wind accretion models.

Findings

CEMP star fraction modestly increases with WRLOF

Significant differences in carbon distribution among CEMP stars

Altered period distribution in CEMP star population

Abstract

Carbon-enhanced metal-poor (CEMP) stars count for 9-25% of all the very metal-poor stars of the halo. In at least some CEMP stars the chemical enrichment is believed to be due to wind mass transfer in the past from an AGB donor star on to a low-mass companion. However, binary population synthesis models predict much lower CEMP fractions. As an alternative to the canonical Bondi-Hoyle-Lyttleton (BHL) wind accretion model, recent hydrodynamical simulations suggest an efficient mode of wind mass transfer, called wind Roche-lobe overflow (WRLOF), can reproduce observations of AGB winds in binary systems. We use our population synthesis model to test the consequences of WRLOF on a population of CEMP stars. Compared to previous predictions based on the BHL model we find a modest increase of the fraction of CEMP stars and substantial differences in the distributions of carbon and periods in the population of CEMP stars.