Are the Bulge C-stars related to the Sagittarius dwarf galaxy?

Part of the mystery around the Bulge carbon stars from Azzopardi et al. (1991) is solved, if they are related to the Sagittarius dwarf galaxy. The carbon stars are in that case 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 carbon stars still have luminosities fainter than the lower LMC limit of M-bol similar or equal to -3(m).5. A similar trend is present among some of the carbon stars found in other dwarf spheroidals, but they do not reach a limit as faint as M-bol similar or equal to -1(m).4 found for the SMC. At present, the TP-AGB models cannot explain the origin of carbon stars with M-bol > -3(m).5 through a single-star evolution scenario? even if they form immediately after entering 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.