Mass-luminosity relation and pulsational properties of Wolf-Rayet stars

TL;DR

This paper investigates the mass-luminosity relation and pulsational behavior of Wolf-Rayet stars, emphasizing the impact of mass loss rates and the iron bump kappa-mechanism on stellar oscillations.

Contribution

It provides new relations for the mass-luminosity connection of Wolf-Rayet stars considering different mass loss scenarios and explores their pulsational properties through hydrodynamic models.

Findings

Oscillation amplitude decreases with stellar mass and mass loss rate.

Pulsations are excited by the iron bump kappa-mechanism at T~2x10^5 K.

Stars with M > 10 M_sun exhibit nonlinear running waves in pulsations.

Abstract

Evolution of Population I stars with initial masses from 70M_\odot to 130M_\odot is considered under various assumptions on the mass loss rate \dot M. The mass-luminosity relation of W-R stars is shown to be most sensitive to the mass loss rate during the helium burning phase \dot M_{3\alpha}. Together with the mass-luminosity relation obtained for all evolutionary sequences several more exact relations are determined for the constant ratio f_{3\alpha}=\dot M/\dot M_{3\alpha} with 0.5 \le f_{3\alpha} \le 3. Evolutionary models of W-R stars were used as initial conditions in hydrodynamic computations of radial nonlinear stellar oscillations. The oscillation amplitude is larger in W-R stars with smaller initial mass or with lower mass loss rate due to higher surface abundances of carbon and oxygen. In the evolving W-R star the oscillation amplitude decreases with decreasing stellar mass M and for M < 10M_\odot the sufficiently small nonlinear effects allow us to calculate the integral of the mechanical work W done over the pulsation cycle in each mass zone of the hydrodynamical model. The only positive maximum on the radial dependence of W is in the layers with temperature of T\sim 2e5K where oscillations are excited by the iron Z--bump kappa-mechanism. Radial oscillations of W-R stars with mass of M > 10M_\odot are shown to be also excited by the kappa-mechanism but the instability driving zone is at the bottom of the envelope and pulsation motions exist in the form of nonlinear running waves propagating outward from the inner layers of the envelope.