tokens: We thank the Gemini Observatory staff for their help with our observing program and the anonymous referee for comments that improved the manuscript. J.W., L.J., L.C.H. and X.W. acknowledge support from the National Key RD Program of China (2016YFA0400702, 2016YFA0400703) and from the National Science Foundation of China (grant No. 11473002, 11533001, 11721303). Y.S. acknowledges support from an Alfred P. Sloan Research Fellowship and National Science Foundation grant No. AST-1715579. D.R. acknowledges support from the National Science Foundation under grant No. AST-1614213. M.V. gratefully acknowledges support from the Independent Research Fund Denmark via grant Nos. DFF 4002-00275 and 8021-00130.
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