tokens: The 1.5-m GREGOR solar telescope was built by a German consortium under the leadership of the Kiepenheuer-Institut für Sonnenphysik in Freiburg with the Leibniz-Institut für Astrophysik Potsdam, the Institut für Astrophysik Göttingen, and the Max-Planck-Institut für Sonnensystemforschung in Göttingen as partners, and with contributions by the Instituto de Astrofísica de Canarias and the Astronomical Institute of the Academy of Sciences of the Czech Republic. We are very grateful to the engineering, operating and technical staff at the GREGOR Telescope: Andreas Fischer, Olivier Grassin, Roberto Simoes, Clements Halbgewachs, Thomas Kentischer, Thomas Sonner, Peter Caligari, Michael Wiessschädel, Frank Heidecke, Stefan Semeraro, and Oliver Wiloth. We are also indebted to Franz Kneer and an anonymous referee for their comments on the paper. A.A.R. acknowledges financial support by the Spanish Ministry of Economy and Competitiveness through project AYA2014-60476-P and the Ramón y Cajal fellowships. This research has made use of NASA’s Astrophysics Data System.
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