Infrared photometry and the comparative stellar content of dwarf spheroidals in the galactic halo

Abstract

Infrared JHK photometry data for carbon stars in the Ursa Minor, Draco, Leo I, and Leo II dwarf spheroidal galaxies and for a number of oxygen-rich giants in these systems are reported. A comparison of the red stellar content in all seven Milky Way spheroidals is made using the photometry results. It is found that, with an exception of Ursa Minor, the most bolometrically luminous stars in all the dwarfs are carbon stars. The two mechanisms suggested to be involved in the formation of carbon stars discussed are related to thermal pulses during the asymptotic giant branch phase and to the binary mass transfer. Interpolation between globular cluster giant branches is used to derive mean abundances for the Ursa Minor, Draco, and Leo systems from the measurements of the oxygen-rich giants. Good agreement of the results with available spectrophotometric measurements, performed using J-K color, is noted.