Are the Bulge C– stars in the Sagittarius dwarf galaxy?

Part of the mystery around the Bulge carbon stars from Azzopardi et al. (1991) is solved, when they belong to the Sagittarius dwarf galaxy. The carbon stars are not metal-rich as previously thought, but they have a metallicity comparable to the LMC, with an age between 0.1 – 1 Gyr. A significant fraction of the Sagittarius dwarf carbon stars have luminosities fainter than the lower LMC and SMC limit of respectively Mbol ≃ −3.5 and Mbol ≃ −3.0. The similar trend is present among some of the carbon stars found in other dwarf spheroidals. At present, the TP-AGB evolution models cannot explain this, even if carbon stars form immediately after they enter the TP-AGB phase. Mass transfer through binary evolution is suggested as a possible scenario to explain the origin of these low luminosity carbon stars.