A binary origin for low-luminosity carbon stars

We show that mass transfer from thermally pulsing asymptotic giant branch stars in binary systems naturally leads to a population of dim, extrinsic carbon stars in the Magellanic Clouds. This explains the existence of the dim tail in the carbon star luminosity functions of the clouds. We also conclude that the majority of these extrinsic stars are first giant-branch stars rather than early asymptotic giant branch stars.