X-Shooting ULLYSES: Massive stars at low metallicity

I. Project description^⋆,⋆⋆

¹ Armagh Observatory and Planetarium, College Hill, BT61 9DG Armagh, UK
e-mail: jorick.vink@armagh.ac.uk
² ESO – European Organisation for Astronomical Research in the Southern Hemisphere, Alonso de Cordova 3107, Vitacura, Santiago de Chile, Chile
e-mail: amehner@eso.org
³ Dept of Physics & Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, UK
e-mail: paul.crowther@sheffield.ac.uk
⁴ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁵ Penn State Scranton, 120 Ridge View Drive, Dunmore, PA 18512, USA
⁶ Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁷ Institute for Computational Cosmology, Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK
⁸ Department of Physics and Astronomy, East Tennessee State University, Johnson City, TN 37614, USA
⁹ Department of Physics and Astronomy & Pittsburgh Particle Physics, Astrophysics and Cosmology Center (PITT PACC), University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260, USA
¹⁰ Astronomický ústav, Akademie věd České republiky, 251 65 Ondřejov, Czech Republic
¹¹ Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain
¹² Dpto. Astrofisica, Universidad de La Laguna, 38 205 La Laguna, Tenerife, Spain
¹³ Argelander Institute für Astronomie der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁴ LUPM, Université de Montpellier, CNRS, Place Eugène Bataillon, 34095 Montpellier, France
¹⁵ ESO – European Organisation for Astronomical Research in the Southern Hemisphere, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
¹⁶ Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile
¹⁷ Anton Pannekoek Institute for Astronomy, Universiteit van Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁸ Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands
¹⁹ Center for Computational Astrophysics, Division of Science, National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
²⁰ Zentrum für Astronomie der Universität Heidelberg, Rechen-Institut, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
²¹ NAT – Universidade Cidade de Sao Paulo, Rua Galvao Bueno, 868, São Paulo, Brazil
²² Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
²³ Fakultät für Physik, Universität Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
²⁴ Gemini Observatory/NSF’s NOIRLab, Casilla 603, La Serena, Chile
²⁵ University of Michigan, Department of Astronomy, 323 West Hall, Ann Arbor, MI 48109, USA
²⁶ Institute for Physics and Astronomy, University Potsdam, 14476 Potsdam, Germany
²⁷ Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, CA 93106, USA
²⁸ European Space Agency (ESA), ESA Office, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²⁹ Centro de Astrobiología (CAB), CSIC-INTA, Campus ESAC. C. bajo del castillo s/n, 28 692 Madrid, Spain
³⁰ Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany
³¹ Center for Astrophysics and Space Astronomy, University of Colorado Boulder, Boulder, CO 80309-0389, USA
³² Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
³³ Département de physique, Université de Montréal, Campus MIL, 1375 Thérèse-Lavoie-Roux, Montréal, (QC) H2V 0B3, Canada
³⁴ Royal Observatory of Belgium, Avenue circulaire/Ringlaan 3, 1180 Brussels, Belgium
³⁵ Rutgers University, Department of Physics and Astronomy, 136 Frelinghuysen Road, Piscataway, NJ 08854, USA
³⁶ Lennard-Jones Laboratories, Keele University, Keele ST5 5BG, UK
³⁷ The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, CA 91101 Pasadena, USA
³⁸ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. Torrejón a Ajalvir km 4., 28850 Torrejón de Ardoz, Madrid, Spain
³⁹ Departamento de Física Aplicada, Universidad de Alicante, 03 690, San Vicente del Raspeig, Alicante, Spain
⁴⁰ Department of Physics and Astronomy, Howard University, Washington, DC 20059, USA
⁴¹ Observatório do Valongo, Universidade Federal do Rio de Janeiro, Ladeira Pedro Antônio 43, Rio de Janeiro, CEP 20080-090, Brazil
⁴² Instituto de Astrofísica de Andalucía – CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁴³ Center for Research and Exploration in Space Science and Technology, and X-ray Astrophysics Laboratory, NASA/GSFC, Greenbelt, MD 20771, USA
⁴⁴ Space Telescope Science Institute, 3700 San Martin Dr, Baltimore, MD 21218, USA
⁴⁵ Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴⁶ Max Planck Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85741 Garching, Germany
⁴⁷ Centro Universitário FEI, Dept. de Física. Av. Humberto Alencar de Castelo Branco, 3972, São Bernardo do Campo, SP, CEP 09850-901, Brazil
⁴⁸ IAASARS, National Observatory of Athens, 15236 Penteli, Greece
⁴⁹ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
⁵⁰ Instituto de Astronomía, Universidad Nacional Autónoma de México, Unidad Académica en Ensenada, Km 103 Carr. Tijuana-Ensenada, Ensenada, B.C. CP 22860, Mexico
⁵¹ National Solar Observatory, 22 Ohi‘a Ku St, Makawao, HI 96768, USA
⁵² Institute of Astrophysics, FORTH, 71110 Heraklion, Greece
⁵³ Yunnan Observatories, Chinese Academy of Sciences, Kunming, 650216 Yunnan, PR China

Received: 8 December 2022
Accepted: 5 May 2023

Abstract

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 ESO’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.