High-resolution X-ray spectroscopy of the stellar wind in Vela X-1 during a flare

V.G. is supported through the Margarete von Wrangell fellowship by the ESF and the Ministry of Science, Research and the Arts Baden-Wurttemberg. We acknowledge support from the ESTEC Faculty Visiting Scientist Programme to V.G. S.B. acknowledges financial support from the Italian Space Agency under grant ASI-INAF 2017-14-H.O. Work at LLNL was performed under the auspieces of the U.S. Department of Energy under contract No. DE-AC52-07NA27344. S.M.N. acknowledges funding by the Spanish Ministry MCIU under project RTI2018-096686-B-C21 (MCIU/AEI/FEDER, UE), co-funded by FEDER funds and by the Unidad de Excelencia Maria de Maeztu, ref. MDM-2017-0765.