7460 20250204104803.0 10.1051/0004-6361/202245588 DOI SCART-2025-0091 Hawcroft, C. X-Shooting ULLYSES: Massive stars at low metallicity. III. Terminal wind speeds of ULLYSES massive stars 2024 Context. The winds of massive stars have a significant impact on stellar evolution and on the surrounding medium. The maximum speed reached by these outflows, the terminal wind speed v∞, is a global wind parameter and an essential input for models of stellar atmospheres and feedback. With the arrival of the ULLYSES programme, a legacy UV spectroscopic survey with the Hubble Space Telescope, we have the opportunity to quantify the wind speeds of massive stars at sub-solar metallicity (in the Large and Small Magellanic Clouds, 0.5 Z⊙ and 0.2 Z⊙, respectively) at an unprecedented scale. Aims: We empirically quantify the wind speeds of a large sample of OB stars, including supergiants, giants, and dwarfs at sub-solar metallicity. Using these measurements, we investigate trends of v∞ with a number of fundamental stellar parameters, namely effective temperature (Teff), metallicity (Z), and surface escape velocity vesc. Methods: We empirically determined v∞ for a sample of 149 OB stars in the Magellanic Clouds either by directly measuring the maximum velocity shift of the absorption component of the C IV λλ1548-1550 line profile, or by fitting synthetic spectra produced using the Sobolev with exact integration method. Stellar parameters were either collected from the literature, obtained using spectral-type calibrations, or predicted from evolutionary models. Results: We find strong trends of v∞ with Teff and vesc when the wind is strong enough to cause a saturated P Cygni profile in C IV λλ1548-1550. We find evidence for a metallicity dependence on the terminal wind speed v∞ ∝ Z0.22±0.03 when we compared our results to previous Galactic studies. Conclusions: Our results suggest that Teff rather than vesc should be used as a straightforward empirical prediction of v∞ and that the observed Z dependence is steeper than suggested by earlier works. NO Sana, H. Mahy, L. Sundqvist, J. O. de Koter, A. Crowther, P. A. Bestenlehner, J. M. Brands, S. A. David-Uraz, A. Decin, L. Erba, C. Garcia, M. Hamann, W. -R. Herrero, A. Ignace, R. Kee, N. D. Kubátová, B. Lefever, R. Moffat, A. Najarro, F. Oskinova, L. Pauli, D. Prinja, R. Puls, J. Sander, A. A. C. Shenar, T. St-Louis, N. ud-Doula, A. Vink, J. S. Astronomy & Astrophysics 688 2024 A105 19 laurent.mahy@ksb-orb.be 2582274 http://publi2-as.oma.be/record/7460/files/Hawcroft_XshootU_2024.pdf 3132 http://publi2-as.oma.be/record/7460/files/Hawcroft_XshootU_2024.gif?subformat=icon icon 4004 http://publi2-as.oma.be/record/7460/files/Hawcroft_XshootU_2024.jpg?subformat=icon-180 icon-180 published in REFERD