Stellar Archaeology in the Galactic halo with Ultra-Faint Dwarfs: VII. Hercules
| Autor: | 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, Márcio, Grado, Aniello, Limatola, Luca, Smith, Horace A., Kinemuchi, Karen |
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| Rok vydání: | 2012 |
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| Druh dokumentu: | Working Paper |
| DOI: | 10.1088/0004-637X/756/2/121 |
| Popis: | 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 6 fundamental-mode (ab-type) and 3 first overtone (c-type) RR Lyrae stars, and one Anomalous Cepheid. The average period of the ab-type RR Lyrae stars, < Pab >= 0.68 d (sigma = 0.03 d), 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)o = 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' {\times} 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 clusters M68. Comment: 28 pages, 7 figures, Accepted for publication in ApJ |
| Databáze: | arXiv |
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