The red giant branch tip and bump of the Leo II dwarf spheroidal galaxy |
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Authors: | M. Bellazzini N. Gennari F. R. Ferraro |
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Affiliation: | INAF –Osservatorio Astronomico di Bologna, via Ranzani 1, 40127, Bologna, Italy;Universitàdi Bologna –Dipartimento di Astronomia, via Ranzani 1, 40127, Bologna, Italy |
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Abstract: | We present V and I photometry of a 9.4 × 9.4 arcmin2 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 (B1, 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 (B1) 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. |
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Keywords: | stars: Population II stars: variables: other galaxies: distances and redshifts Local Group |
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