The red giant branch tip and bump of the Leo II dwarf spheroidal galaxy

Abstract

We present V and I photometry of a 9.4 x 9.4 arcmin 2 field centred on the dwarf spheroidal galaxy Leo II. The tip of the red giant branch (TRGB) is identified at I TRGB = 17.83 ± 0.03 and adopting ([M/H]) = -1.53 ± 0.2 from the comparison of RGB stars with Galactic templates, we obtain a distance modulus (m - M) 0 = 21.84 ± 0.13, corresponding to a distance D = 233 ± 15 kpc. Two significant bumps have been detected in the luminosity function of the RGB. The fainter bump (Bl, at V = 21.76 ± 0.05) is the RGB bump of the dominant stellar population while the actual nature of the brightest one (B2, at V = 21.35 ± 0.05) cannot be firmly assessed on the basis of the available data; it may be due to the asymptotic giant branch clump of the main population or it may be a secondary RGB bump. The luminosity of the main RGB bump (Bl) suggests that the majority of RGB stars in Leo II belong to a population that is ≥4 Gyr younger than the classical Galactic globular clusters. The stars belonging to the He-burning red clump are shown to be significantly more centrally concentrated than RR Lyrae and blue horizontal branch stars, probing the existence of an age/metallicity radial gradient in this remote dwarf spheroidal.