X-Shooting ULLYSES: Massive stars at low metallicity XV. On the metallicity dependence of B-supergiant mass-loss rates

Abstract

Context. For stellar evolution models we rely on mass-loss rate prescriptions that show features that lack empirical confirmation, such as the bi-stability jump. This jump is an increase in mass loss in the decreasing temperature regime Teff 28-21 kK. Although papers compared empirical results to prescriptions,a large observational sample of B stars for which the wind has been scrutinised over different metallicities is still lacking. Aims. By modelling of both ultraviolet (ULLYSES) and optical (XShootU) spectra, we determined the stellar and wind parameters, of 24 SMC B stars ranging in Teff from 13 to 29 kK. By combining this sample with LMC studies, we compared the wind behaviour of B stars in two different metallicity regimes. We compared our results to common mass-loss rate prescriptions to test features present in these models and their metallicity dependence. Methods. We have used the model atmosphere code fastwind and the genetic algorithm code Kiwi-GA to fit the UV and optical spectra simultaneously. This allows us to determine wind properties including clumping behaviour. Results. The metallicity trends present in the mass-loss prescriptions (Z^(0.41-1.4)) explored here overestimate the empirical metallicity dependence in the B-star regime, which appears very weak. We do not find an increase in mass-loss rate at approximately spectral type B1. We show that on average 40% of the wind mass is located in the wind medium between the clumps. We compiled a sample of 80+ O and B stars in the SMC and LMC. From a comparison we find a clear difference in O- and B-type metallicity dependence. Conclusions. The lack of a bi-stability jump in the B-star regime and a weak metallicity dependence for the same stars offers new empirical constraints to models of line-driven winds. As differences between these models are large (reaching orders of magnitude) such constraints are much needed.

References in corpus (34)

• The empirical metallicity dependence of the mass-loss rate of O- and early B-type stars
• Bright OB stars in the Galaxy - III. Constraints on the radial stratification of the clumping factor in hot star winds from a combined Halpha, IR and radio analysis
• A cosmic abundance standard: chemical homogeneity of the solar neighbourhood and the ISM dust-phase composition
• Bright OB stars in the Galaxy IV. Stellar and wind parameters of early to late B supergiants
• New predictions for radiation-driven, steady-state mass-loss and wind-momentum from hot, massive stars II. A grid of O-type stars in the Galaxy and the Magellanic Clouds
• Constraining mixing in massive stars in the Small Magellanic Cloud
• Theory and Diagnostics of Hot Star Mass Loss
• Metallicity-dependent wind parameter predictions for OB stars
• X-Shooting ULLYSES: massive stars at low metallicity. I. Project Description
• First 3D Radiation-Hydrodynamic Simulations of Wolf-Rayet Winds
• LMC Blue Supergiant Stars and the Calibration of the Flux-weighted Gravity--Luminosity Relationship
• Empirical mass-loss rates and clumping properties of Galactic early-type O supergiants
• The properties of ten O-type stars in the low-metallicity galaxies IC 1613, WLM and NGC 3109
• On the Importance of the Interclump Medium for Superionization: O VI Formation in the Wind of Zeta Pup
• X-Shooting ULLYSES: Massive stars at low metallicity. III. Terminal wind speeds of ULLYSES massive stars
• Binarity at LOw Metallicity (BLOeM): a spectroscopic VLT monitoring survey of massive stars in the SMC
• Atmospheric NLTE models for the spectroscopic analysis of blue stars with winds. V. Complete comoving frame transfer, and updated modeling of X-ray emission
• New mass-loss rates of B supergiants from global wind models
• Upper Mass-Loss Limits and Clumping in the Intermediate and Outer Wind Regions of OB stars
• The IACOB project X. Large-scale quantitative spectroscopic analysis of Galactic luminous blue stars
• X-Shooting ULLYSES: Massive Stars at low metallicity II. DR1: Advanced optical data products for the Magellanic Clouds
• X-Shooting ULLYSES: Massive Stars at low metallicity IX: Empirical constraints on mass-loss rates and clumping parameters for OB supergiants in the Large Magellanic Cloud
• Impact of main-sequence mass loss on the appearance, structure and evolution of Wolf-Rayet stars
• The IACOB project XI. No increase of mass-loss rates over the bistability region
• X-Shooting ULLYSES: Massive stars at low metallicity. IV. Spectral analysis methods and exemplary results for O stars
• Method and new tabulations for flux-weighted line-opacity and radiation line-force in supersonic media
• Empirical mass-loss rates and clumping properties of O-type stars in the LMC
• Theoretical wind clumping predictions from 2D LDI models of O-star winds at different metallicities
• Evolution of rotating massive stars adopting a newer, self-consistent wind prescription at SMC metallicity
• Binarity at LOw Metallicity (BLOeM): Multiplicity of early B-type supergiants in the Small Magellanic Cloud
• X-Shooting ULLYSES: Massive Stars at Low Metallicity: XI. Pipeline-determined Physical Properties of Magellanic Cloud OB Stars
• X-Shooting ULLYSES: massive stars at low metallicity: XII. The clumped winds of O-type (super)giants in the Large Magellanic Cloud
• X-Shooting ULLYSES: Massive stars at low metallicity. XIII. Putting the bi-stability jump to the test in the LMC
• An on-the-fly line-driven-wind iterative mass-loss estimator (LIME) for hot, massive stars of arbitrary chemical compositions