Dupree, A. K.Dotter, AaronJohnson, C. I.Marino, Anna FabiolaMilone, Antonino P.Bailey III, J. I.Crane, J. D.Mateo, MarioOlszewski, Edward W.2020-12-202020-12-202041-8205http://hdl.handle.net/1885/218257High-resolution spectroscopic observations were taken of 29 extended main-sequence turnoff (eMSTO) stars in the young (~200 Myr) Large Magellanic Cloud (LMC) cluster, NGC 1866, using the Michigan/Magellan Fiber System and MSpec spectrograph on the Magellan-Clay 6.5 m telescope. These spectra reveal the first direct detection of rapidly rotating stars whose presence has only been inferred from photometric studies. The eMSTO stars exhibit Hα emission (indicative of Be-star decretion disks), others have shallow broad Hα absorption (consistent with rotation gsim150 km s−1), or deep Hα core absorption signaling lower rotation velocities (lesssim150 km s−1). The spectra appear consistent with two populations of stars—one rapidly rotating, and the other, younger and slowly rotating.A.F.M. and A.P.M. acknowledge support by the Australian Research Council through Discovery Early Career Researcher Awards DE160100851 and DE150101816. E.W.O. was partially supported by NSF grant AST1313006.application/pdfen-AU© 2017 The American Astronomical Society2017-08-2310.3847/2041-8213/aa85dd2020-11-23