Variable stars in local group galaxies - IV. RR Lyrae stars in the central regions of the low-density galaxy Crater II

M. Monelli , A. R. Walker , C. E. Martínez-Vázquez , P. B. Stetson , C. Gallart , E. J. Bernard (1) , G. Bono , A. K. Vivas , G. Andreuzzi , M. Dall'Ora , G. Fiorentino , A. Dorta

1 OCA - Observatoire de la Côte d'Azur

We present a search and analysis of variable stars in the recently discovered Crater II dwarf galaxy. Based on B, V, I data collected with the Isaac Newton Telescope (FoV∼0.44 deg²), we detected 37 variable stars, of which 34 are bone-fide RR Lyrae stars of Crater II (28 RRab, 4 RRc, 2 RRd). We applied the metal-independent (V, B - V) Period-Wesenheit relation and derived a true distance modulus (μ = 20.30 ± 0.08 mag (σ = 0.16 mag). Individual metallicities for RR Lyrae stars were derived by inversion of the predicted I-band Period-Luminosity relation. We find a mean metallicity of [Fe/H] = -1.64 and a standard deviation of σ _{[Fe/H]}=0.21 dex, compatible with either negligible or vanishing intrinsic metallicity dispersion. The analysis of the colour-magnitude diagram reveals a stark paucity of blue horizontal branch stars, at odds with other Galactic dwarfs, and globular clusters with similar metal abundances.

Mots clés: stars: general; stars: horizontal branch; stars: variables: RR Lyrae; galaxies: evolution; Local Group; Astrophysics - Astrophysics of Galaxies

Domaines: Planète et Univers [physics]; Astrophysique [astro-ph]

M. Monelli, A. R. Walker, C. E. Martínez-Vázquez, P. B. Stetson, C. Gallart, et al.. Variable stars in local group galaxies - IV. RR Lyrae stars in the central regions of the low-density galaxy Crater II. Monthly Notices of the Royal Astronomical Society, 2018, 479, pp.4279-4291. ⟨10.1093/mnras/sty1645⟩. ⟨insu-03689234⟩