Theoretical wind clumping predictions from 2D LDI models of O-star winds at different metallicities

Abstract

Hot, massive (OB) stars experience strong line-driven stellar winds and mass loss. As the majority of efficient driving lines are metallic, the amount of wind driving and mass loss is dependent on the stellar metallicity Z. In addition, line-driven winds are intrinsically inhomogeneous and clumpy. However, to date, neither theoretical nor empirical studies of line-driven winds have investigated how such wind clumping may also depend on Z. We theoretically investigated the degree of wind clumping due to the line-deshadowing instability (LDI) as a function of Z. We performed two-dimensional hydrodynamic simulations of the LDI with an assumed one-dimensional radiation line force for a grid of O-star wind models with fixed luminosity, but with different metal contents by varying the accumulative line strength Qbar describing the total ensemble of driving lines. We find that, for this fixed luminosity, the amount of wind clumping decreases with metallicity. The decrease is clearly seen in the statistical properties of our simulations, but is nonetheless rather weak; a simple power-law fit for the dependence of the clumping factor f_cl = <rho^2>/<rho>^2 on metallicity yields f_cl ~ Z^(0.15 +/- 0.01). This implies that empirically derived power-law dependencies of mass-loss rate Mdot on metallicity -- which were previously inferred from spectral diagnostics effectively depending on Mdot*sqrt(f_cl) but without having any constraints on f_cl(Z) -- should be only modestly altered by clumping. We expect that this prediction can be directly tested using new data from the Hubble Space Telescope Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) project.

accepted for publication in A&A

References in corpus (13)

• Mass loss from hot massive stars
• 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
• Mass loss from late-type WN stars and its Z-dependence: very massive stars approaching the Eddington limit
• Metallicity-dependent wind parameter predictions for OB stars
• Empirical mass-loss rates and clumping properties of Galactic early-type O supergiants
• Theoretical wind clumping predictions of OB supergiants from line-driven instability simulations across the bi-stability jump
• Dynamically inflated wind models of classical Wolf-Rayet stars
• Upper Mass-Loss Limits and Clumping in the Intermediate and Outer Wind Regions of OB stars
• Radiation-Hydrodynamics with MPI-AMRVAC: Flux-Limited Diffusion
• Wind properties of Milky Way and SMC massive stars: empirical Z dependence from CMFGEN models
• Shock-heated radiation-driven outflows as a solution to the weak-wind problem of late O-type stars
• Simulations of the line-driven instability in magnetic hot star winds

Cited by in corpus (8)

• Empirical mass-loss rates and clumping properties of O-type stars in the LMC
• Evolution of rotating massive stars adopting a newer, self-consistent wind prescription at SMC metallicity
• Inverse Compton cooling of thermal plasma in colliding-wind binaries
• X-Shooting ULLYSES: massive stars at low metallicity: XII. The clumped winds of O-type (super)giants in the Large Magellanic Cloud
• Optically-thick Structure in Early B Type Supergiant Stellar Winds at Low Metallicities
• Clumpy wind studies and the non-detection of cyclotron line in OAO 1657-415
• X-Shooting ULLYSES: Massive stars at low metallicity XV. On the metallicity dependence of B-supergiant mass-loss rates
• Novel application to estimate the mass-loss and the dust-formation rates in O-type gamma-ray binaries using near-infrared photometry