Wind properties of Milky Way and SMC massive stars: empirical Z dependence from CMFGEN models

Abstract

Detailed knowledge about stellar winds and evolution at different metallicities is crucial for understanding stellar populations and feedback in the Local Group of galaxies and beyond. Despite efforts in the literature, we still lack a comprehensive, empirical view of the dependence of wind properties on metallicity ($Z$). Here, we investigate the winds of O and B stars in the Milky Way (MW) and Small Magellanic Cloud (SMC). We gathered a sample of 96 stars analyzed by means of the NLTE code CMFGEN. We explored their wind strengths and terminal velocities to address the $Z$ dependence, over a large luminosity range. The empirical wind-luminosity relation (WLR) obtained updates and extends previous results in the literature. It reveals a luminosity and $Z$ dependence, in agreement with the radiatively driven wind theory. For bright objects ($\log L/L_{\odot }\gtrsim 5.4$), we infer that $\dot{M}\sim Z^{0.5-0.8}$. However, this dependence seems to get weaker or vanish at lower luminosities. The analysis of the terminal velocities suggests a shallow $Z^n$ dependence, with $n\sim 0.1-0.2$, but it should be confirmed with a larger sample and more accurate $V_{\infty }$ determinations. Recent results on SMC stars based on the PoWR code support our inferred WLR. On the other hand, recent bow-shocks measurements stand mostly above our derived WLR. Theoretical calculations of the WLR are not precise, specially at low $L$, where the results scatter. Deviations between our results and recent predictions are identified to be due to the weak wind problem and the extreme terminal velocities predicted by the models. The Z dependence suggested by our analysis deserves further investigations, given its astrophysical implications.

17 Pages, 10 Figures and 3 Tables, accepted for publication in MNRAS

References in corpus (17)

• The empirical metallicity dependence of the mass-loss rate of O- and early B-type stars
• An XMM-Newton view of the young open cluster NGC 6231 -- II. The OB star population
• Quantitative studies of the optical and UV spectra of Galactic early B supergiants I. Fundamental parameters
• High resolution X-ray spectroscopy of bright O type stars
• Testing massive star evolution, star-formation history and feedback at low metallicity : Spectroscopic analysis of OB stars in the SMC Wing
• Metallicity-dependent wind parameter predictions for OB stars
• New predictions for radiation-driven, steady-state mass-loss and wind-momentum from hot, massive stars. I. Method and first results
• Direct spectroscopic observations of clumping in O-star winds
• Winds of low-metallicity OB-type stars: HST-COS spectroscopy in IC1613
• No breakdown of the radiatively-driven wind theory in low-metallicity environments
• A spectroscopic investigation of the O-type star population in four Cygnus OB associations. II. Determination of the fundamental parameters
• Radial dependence of line profile variability in seven O9--B0.5 stars
• Massive stars in the Small Magellanic Cloud : Evolution, rotation and surface abundances
• Shock-heated radiation-driven outflows as a solution to the weak-wind problem of late O-type stars
• Mid-infrared observations of O-type stars: spectral morphology
• Using Shell Models to Investigate Clumping in the Wind of the O7Iaf+ Supergiant AzV83
• Models for Weak Wind and Momentum Problems in the Winds of Hot Stars

Cited by in corpus (4)

• Quantitative spectroscopy of late O-type main-sequence stars with a hybrid non-LTE method
• Reverse Algols and hydrogen-rich Wolf-Rayet stars from very massive binaries
• Momentum and energy injection by a wind-blown bubble into an inhomogeneous interstellar medium
• A near-UV reconnaissance of metal-poor massive stars