Hydrogen-free Wolf-Rayet stars: Helium stars with envelope-inflation structure and rotation

Abstract

Observations have shown that the effective temperature of hydrogen-free Wolf-Rayet (WR) stars is considerably lower than that of the standard model, which means that the radius of the observed H-free WR stars is several times larger than that estimated by the standard model. The envelope inflation structure (EIS) caused by the radiation luminosity being close to the Eddington luminosity in the iron opacity peak region of H-free WR stars may be the key to resolve the radius problem of H-free WR stars. We try to explain the H-free WR stars observed in the Milk Way (MW) and the Large Magellanic Cloud (LMC) by the He stars. Using the Modules for Experiments in Stellar Astrophysics code, we compute the evolution of He stars with and without MLT++ prescriptions and discuss their effects on the EIS. We have calculated the evolution of He stars using a new mass-loss rate formula and three different relative rotational velocity and compared our results with observations on Hertzsprung-Russell diagrams. The low luminosity (log$(L/L_{\odot })\le 5.2$) H-free WR stars in the MW and the LMC can be explained by the helium giant phase in low-mass He stars, the high $X_C$ and $X_O$ in WC stars can only evolve through low-mass He stars with a rapid rotation. High-mass He stars with the EIS can explain H-free WR stars with a luminosity exceeding $10^{5.7}{L}_{\odot }$ and an effective temperature above $10^{4.7}$ K in the MW. They can also explain H-free WR stars on the right-hand side of the He zero-age main sequence in the LMC. High-mass stars with the EIS evolve into WO stars at the final evolution stage, and the shorter lifetime fraction is consistent with the small number of observed WO stars.

9 pages, 7 figures 1 tables, Accepted to A&A

References in corpus (20)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Physical Properties of Wolf-Rayet Stars
• The Galactic WC stars: Stellar parameters from spectral analyses indicate a new evolutionary sequence
• On the nature of massive helium star winds and Wolf-Rayet-type mass loss
• The Galactic WN stars revisited. Impact of Gaia distances on fundamental stellar parameters
• Winds from stripped low-mass Helium stars and Wolf-Rayet stars
• Rotating massive O stars with non-spherical 2D winds
• First 3D Radiation-Hydrodynamic Simulations of Wolf-Rayet Winds
• A new prescription for the mass-loss rates of WC and WO stars
• The temperature dependency of Wolf-Rayet-type mass loss: An exploratory study for winds launched by the hot iron bump
• Dynamically inflated wind models of classical Wolf-Rayet stars
• Stripped-Envelope Stars in Different Metallicity Environments I. Evolutionary Phases, Classification and Populations
• Effects of Irradiation on the Evolution of Ultra-compact X-ray Binaries
• A systematic study of super-Eddington layers in the envelopes of massive stars
• Centrifugally Driven Mass Loss and Outbursts of Massive Stars
• Possible Formation Scenarios of ZTF J153932.16+502738.8-A Gravitational Source Close to the Peak of LISA's Sensitivity
• Exploring the influence of different velocity fields on Wolf-Rayet star spectra
• The Wolf-Rayet Stellar Response To The Iron Opacity Bump: Envelope Inflation, Winds, and Microturbulence
• Effects of the core-collapse supernova ejecta impact on a rapidly rotating massive companion star
• Intrinsic polarization of Wolf-Rayet stars due to the rotational modulation of the stellar wind

Cited by in corpus (3)

• The population synthesis of Wolf-Rayet stars involving binary merger channels
• A possible formation scenario of the Gaia ID 3425577610762832384: inner binary merger inside a triple common envelope
• Adiabatic Mass Loss In Binary Stars. VI. Massive Helium Binary Stars