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Paper: A New Study of the Variable Star Population in the Hercules Globular Cluster (M13, NGC 6205)
Volume: 529, RR Lyrae/Cepheid 2019: Frontiers of Classical Pulsators
Page: 179
Authors: Deras, D.; Ferro, A. A.; Lázaro, C.; Fierro, I. H. B.; Calderón, J. H.; Muneer, S.; Giridhar, S.
Abstract: We present the results from VI CCD time-series photometry of the globular cluster M13 (NGC 6205). From the Fourier decomposition of the light curves of RRab and RRc stars we found an average metallicity of [Fe/H]zw = -1.58 ± 0.09. The distance to the cluster was estimated as 7.1 ± 0.1 kpc from independent methods related to the variable star families RR Lyrae, SX Phe and W Virginis, from the luminosity of the theoretical ZAHB and from the orbit solution of a newly discovered contact binary star. The RR Lyrae pulsation modes are segregated by the red edge of the first overtone instability strip in this OoII type cluster. A membership analysis of 52,800 stars in the field of the cluster is presented based on Gaia-DR2 proper motions which enabled the recognition of 23,070 likely cluster members, for 7630 of which we possess VI photometry. The identification of member stars allowed the construction of a clean CMD and a proper ZAHB and isochrone fitting, consistent with a reddening, age and distance of 0.02 mag, 12.6 Gyrs and 7.1 kpc respectively. We report seven new variables; one RRc, two SX Phe stars, three SR and one contact binary. V31 presents double-mode nature, and we confirm V36 as RRd.
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