Journal
ASTROPHYSICAL JOURNAL
Volume 756, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/756/2/121
Keywords
galaxies: dwarf; galaxies: individual (Hercules); stars: distances; stars: variables: general; stars: variables: RR Lyrae; techniques: photometric
Categories
Funding
- COFIS ASI-INAF [I/016/07/0]
- ASI-INAF [I/009/10/0]
- PRIN INAF (PI: G. Clementini)
- Proyecto Fondecyt [1110326]
- BASAL Center for Astrophysics and Associated Technologies [PFB-06]
- FONDAP Center for Astrophysics [15010003]
- Chilean Ministry for the Economy, Development, and Tourism's Programa Iniciativa Cientifica Milenio [P07-021-F]
- Milky Way Millennium Nucleus
- Proyecto Anillo
- U.S. NSF [AST0607249, AST0707756]
- STFC [PP/E001149/1, ST/H002391/1, ST/G009465/1, ST/J001465/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/H002391/1, ST/J001465/1, ST/G009465/1, PP/E001149/1] Funding Source: researchfish
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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, < P-ab > = 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 similar to 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.
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