tokens: ACKNOWLEDGEMENTS We are thankful to the anonymous referee for his/her valuable comments. This article is based on observations made in the Observatorios de Canarias del IAC with the William Herschel Telescope (WHT) operated on the island of La Palma by the Isaac Newton Group in the Observatorio del Roque de los Muchachos. This work is partly financed by the Spanish Ministry of Economics and Competitiveness through grants ESP2013-48391-C4-2-R and AYA2016-79425-C3-2-P.
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