X-Shooting ULLYSES: Massive stars at low metallicity: I. Project description

Jorick S. Vink, A. Mehner, P. A. Crowther, A. Fullerton, M. Garcia, F. Martins, N. Morrell, L. M. Oskinova, N. St-Louis, A. Ud-Doula, A. A.C. Sander, H. Sana, J. C. Bouret, B. Kubátová, P. Marchant, L. P. Martins, A. Wofford, J. Th Van Loon, O. Grace Telford, Y. GötbergD. M. Bowman, C. Erba, V. M. Kalari, M. Abdul-Masih, T. Alkousa, F. Backs, C. L. Barbosa, S. R. Berlanas, M. Bernini-Peron, J. M. Bestenlehner, R. Blomme, J. Bodensteiner, S. A. Brands, C. J. Evans, A. David-Uraz, F. A. Driessen, K. Dsilva, S. Geen, V. M.A. Gómez-González, L. Grassitelli, W. R. Hamann, C. Hawcroft, A. Herrero, E. R. Higgins, D. John Hillier, R. Ignace, A. G. Istrate, L. Kaper, N. D. Kee, C. Kehrig, Z. Keszthelyi, J. Klencki, A. De Koter, R. Kuiper, E. Laplace, C. J.K. Larkin, R. R. Lefever, C. Leitherer, D. J. Lennon, L. Mahy, J. Maíz Apellániz, G. Maravelias, W. Marcolino, A. F. McLeod, S. E. De Mink, F. Najarro, M. S. Oey, T. N. Parsons, D. Pauli, M. G. Pedersen, R. K. Prinja, V. Ramachandran, M. C. Ramírez-Tannus, G. N. Sabhahit, A. Schootemeijer, S. Reyero Serantes, T. Shenar, G. S. Stringfellow, N. Sudnik, F. Tramper, L. Wang

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Observations of individual massive stars, super-luminous supernovae, gamma-ray bursts, and gravitational wave events involving spectacular black hole mergers indicate that the low-metallicity Universe is fundamentally different from our own Galaxy. Many transient phenomena will remain enigmatic until we achieve a firm understanding of the physics and evolution of massive stars at low metallicity (Z). The Hubble Space Telescope has devoted 500 orbits to observing ∼250 massive stars at low Z in the ultraviolet (UV) with the COS and STIS spectrographs under the ULLYSES programme. The complementary X-Shooting ULLYSES (XShootU) project provides an enhanced legacy value with high-quality optical and near-infrared spectra obtained with the wide-wavelength coverage X-shooter spectrograph at ESOa's Very Large Telescope. We present an overview of the XShootU project, showing that combining ULLYSES UV and XShootU optical spectra is critical for the uniform determination of stellar parameters such as effective temperature, surface gravity, luminosity, and abundances, as well as wind properties such as mass-loss rates as a function of Z. As uncertainties in stellar and wind parameters percolate into many adjacent areas of astrophysics, the data and modelling of the XShootU project is expected to be a game changer for our physical understanding of massive stars at low Z. To be able to confidently interpret James Webb Space Telescope spectra of the first stellar generations, the individual spectra of low-Z stars need to be understood, which is exactly where XShootU can deliver.

Original languageEnglish
Article numberA154
JournalAstronomy and Astrophysics
StatePublished - 1 Jul 2023
Externally publishedYes


FundersFunder number
Centro de Astrobiología
Spanish Government Ministerio de Ciencia e InnovaciónPGC2018-095 049-B-C22
State Agency of ResearchMCIN/AEI/10.13039/501100011033
National Science FoundationAST-2009412
National Science Foundation
National Aeronautics and Space AdministrationNAS 5-26555
National Aeronautics and Space Administration
Horizon 2020 Framework Programme772086
Horizon 2020 Framework Programme
Space Telescope Science Institute
Natural Sciences and Engineering Research Council of CanadaNAS8-03060, 80NSSC22K0628, TM1-22001B
Natural Sciences and Engineering Research Council of Canada
Science and Technology Facilities CouncilST/V000233/1
Science and Technology Facilities Council
European Research Council
Deutsche Forschungsgemeinschaft445674056, SA4064/1-1
Deutsche Forschungsgemeinschaft
Universität HeidelbergMDM-2017-0737, PID2019-105552RB-C41
Universität Heidelberg
Grantová Agentura České RepublikyGAČR 22-34467S, HST-AR-15794.001-A
Grantová Agentura České Republiky
Fonds Wetenschappelijk Onderzoek1286521N
Fonds Wetenschappelijk Onderzoek
Conselho Nacional de Desenvolvimento Científico e Tecnológico307115/2021-6
Conselho Nacional de Desenvolvimento Científico e Tecnológico
Ministerio de Ciencia e Innovación
Universidad Nacional Autónoma de MéxicoIN106922, 80GSFC21M0002
Universidad Nacional Autónoma de México
European Regional Development Fund


    • Galaxies: dwarf
    • Methods: observational
    • Outflows
    • Stars: atmospheres
    • Stars: early-type
    • Stars: evolution
    • Stars: winds


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