2002MNRAS.335..923M

The first results of a study of the dwarf spheroidal galaxy Leo I using the new Nagoya-South African Infrared Survey Facility (IRSF) are presented. J, H and K_sobservations show that most, if not all, of at least the top magnitude of the asymptotic giant branch (AGB) in K_sis populated by carbon stars. In addition there are five very red objects which are believed to be dust-enshrouded AGB stars. One of these is, remarkably, well outside the main body of the galaxy. Three of these obscured stars and five known carbon stars show variability in observations 11 months apart. One of the obscured stars has ΔK_s= 0.87, making it highly likely that it, at least, is a Mira variable. The tip of the AGB is at M_bol~-5.1, but further variability studies are necessary to obtain a definitive value. Comparison with carbon stars, both Miras and non-Miras, in Magellanic Cloud clusters, and taking into account other evidence on the ages and metallicities of Leo I populations, suggests that these obscured stars belong to the youngest significant population of Leo I and have ages of ∼2 Gyr.