NICER Discovers Spectral Lines during Photospheric Radius Expansion Bursts from 4U 1820−30: Evidence for Burst-driven Winds

T. E. Strohmayer, D. Altamirano, Z. Arzoumanian, P. M. Bult, D. Chakrabarty, J. Chenevez, A. C. Fabian, K. C. Gendreau, S. Guillot, J. J. M. In 't Zand, G. K. Jaisawal, L. Keek, P. Kosec, R. M. Ludlam, S. Mahmoodifar, Christian Malacaria, J. M. Miller