1997A&A...328..211N

Part of the mystery around the Bulge carbon stars from Azzopardi et al. (1991A&AS...88..265A) 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 0.1-1Gyr. A significant fraction of the carbon stars still have luminosities fainter than the lower LMC limit of M_bol≃-3.5mag. 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≃-1.4mag found for the SMC. At present, the TP-AGB models cannot explain the origin of carbon stars with M_bol>-3.5mag 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.