X-Shooting ULLYSES: Massive stars at low metallicity

XII. Clumped winds of O-type (super)giants in the Large Magellanic Cloud

¹ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
² KU Leuven, Instituut voor Sterrenkunde, Celestijnenlaan 200D, 3001 Leuven, Belgium
³ LMU München, Universitätssternwarte, Scheinerstr. 1, 81679 München, Germany
⁴ Astrophysics cluster, School of Mathematical and Physical Sciences, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK
⁵ Departamento de Astrofísica, Centro de Astrobiología, (CSIC-INTA), Ctra. Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁶ School of Chemical, Materials and Biological Engineering, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK
⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁸ Universidad de La Laguna, Departamento de Astrofísica, Avda. Astr. Francisco Sanchez, 38206 La Laguna, Spain
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 Department of Physics & Astronomy, East Tennessee State University, Johnson City, TN 37615, USA
¹¹ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12–14, 69120 Heidelberg, Germany
¹² NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
¹³ Astronomical Institute, Czech Academy of Sciences, Fričova 298, Ondřejov, 251 65, Czech Republic
¹⁴ Royal Observatory of Belgium, Avenue Circulaire/Ringlaan 3, 1180 Brussels, Belgium
¹⁵ Département de physique, Université de Montréal, Complexe des Sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Québec, H2V 0B3, Canada
¹⁶ Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
¹⁷ Armagh Observatory, College Hill, Armagh, BT61 9DG, UK

^★ Corresponding author: s.a.brands@uva.nl

Received: 28 October 2024
Accepted: 10 March 2025

Abstract

Context. Mass loss governs the evolution of massive stars and shapes the stellar surroundings. To quantify the impact of the stellar winds, we need to know the exact mass-loss rates; however, empirical constraints on the rates are hampered by limited knowledge of their small-scale wind structure, also referred to as ‘wind clumping’.

Aims. We aim to improve empirical constraints on the mass loss of massive stars by investigating the clumping properties of their winds, in particular, the relation between stellar parameters and wind structure.

Methods. We analysed the optical and ultraviolet spectra of 25 O-type giants and supergiants in the Large Magellanic Cloud, using the model atmosphere code FASTWIND and a genetic algorithm. We derived the stellar and wind parameters, including detailed clumping properties, such as the amount of clumping, the density of the interclump medium, velocity–porosity of the medium, and wind turbulence.

Results. We obtained stellar and wind parameters for 24 of our sample stars and found that the winds are highly clumped, with an average clumping factor of 〈f_cl〉 = 33 14, an interclump density factor of 〈f_ic〉 = 0.2 0.1, and moderate-to-strong velocity-porosity effects of 〈f_vel〉 = 0.6 0.2. The scatter around the average values of the wind-structure parameters is large. With the exception of a significant, positive correlation between the interclump density factor and mass loss, we find no dependence of clumping parameters on the mass-loss rate or stellar properties.

Conclusions. In the luminosity range we investigate here, the empirical and theoretical mass-loss rates both have a scatter of about 0.5 dex (or a factor 3). Within this uncertainty, the empirical rates and theoretical predictions are in agreement. The origin of the scatter of the empirically inferred mass-loss rates requires further investigation. It is possible that our description of wind clumping is still not sufficient to capture effects of the structured wind, which could contribute to the scatter.