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Date and Time of the Query: 2019-06-17 T13:21:39 PDT
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For refcode 2012ApJ...756..121M:
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2012ApJ...756..121M Stellar Archeology in the Galactic Halo with Ultra-faint Dwarfs. VII. Hercules Musella, Ilaria; Ripepi, Vincenzo; Marconi, Marcella; Clementini, Gisella; Dall'Ora, Massimo; Scowcroft, Victoria; Moretti, Maria Ida; Di Fabrizio, Luca; Greco, Claudia; Coppola, Giuseppina; Bersier, David; Catelan, Marcio; Grado, Aniello; Limatola, Luca; Smith, Horace A.; Kinemuchi, Karen Abstract. We present the first time-series study of the ultra-faint dwarf galaxy Hercules. Using a variety of telescope/instrument facilities we secured about 50 V and 80 B epochs. These data allowed us to detect and characterize 10 pulsating variable stars in Hercules. Our final sample includes six fundamental-mode (ab-type) and three first-overtone (c-type) RR Lyrae stars, and one Anomalous Cepheid. The average period of the ab-type RR Lyrae stars, langP_ab_rang = 0.68 days (sigma = 0.03 days), places Hercules in the Oosterhoff II group, as found for almost the totality of the ultra-faint dwarf galaxies investigated so far for variability. The RR Lyrae stars were used to obtain independent estimates of the metallicity, reddening, and distance to Hercules, for which we find [Fe/H] = -2.30 +/- 0.15 dex, E(B - V) = 0.09 +/- 0.02 mag, and (m - M)_0_ = 20.6 +/- 0.1 mag, in good agreement with the literature values. We have obtained a V, B - V color-magnitude diagram (CMD) of Hercules that reaches V ~ 25 mag and extends beyond the galaxy's half-light radius over a total area of 40' x 36'. The CMD and the RR Lyrae stars indicate the presence of a population as old and metal-poor as (at least) the Galactic globular cluster M68. Based on data collected at the 2.5 m Isaac Newton Telescope, La Palma, Canary Islands, Spain, at the 4.2 m William Herschel Telescope, Roche de los Muchachos, Canary Islands, Spain, at the 2.2 m ESO/MPI telescope, La Silla, Chile, Proposal 079.D-0587, at the 2 m Liverpool Telescope, Roche de los Muchachos, Canary Islands, Spain, and at the 2 m Faulkes Telescope North, Haleakala Observatory, Hawaii, USA. Key words: galaxies: dwarf, galaxies: individual: Hercules, stars: distances, stars: variables: general, stars: variables: RR Lyrae, techniques: photometric
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