Asymptotic giant branch stars in the Sculptor dwarf spheroidal galaxy

Abstract

JHK_S photometry is presented for a 35 arcmin square field centred on the Sculptor dwarf spheroidal galaxy. With the aid of published kinematic data definite galaxy members are identified and the width in J-K of the colour-magnitude diagram is shown to be consistent with an old population of stars with a large range in metal abundance. We identify two Asymptotic Giant Branch variables, both carbon Miras, with periods of 189 and 554 days, respectively, and discuss their ages, metallicities and mass loss as well as their positions in the Mira period-luminosity diagram. There is evidence for a general period-age relation for Local Group Miras. The mass-loss rate for the 554-day variable, MAG29, appears to be consistent with that found for Miras of comparable period in other Local Group galaxies.