The origin of dispersion in the wind mass-loss rate--luminosity relation of massive O stars

Stellar winds of hot stars are accelerated by the radiative force that mainly comes from the line transitions of heavy elements. As a result, the wind mass-loss rate is expected to scale mostly with the stellar luminosity. This scaling clearly emerges from the observational analysis of O stars and their winds, but with substantial scatter. The origin of this scatter is unclear. Part of the scatter of the observational relation between the hot star wind mass-loss rate and luminosity may originate from the sensitivity of the mass-loss rate to other stellar parameters besides the luminosity, such as the effective temperature, mass, and metallicity. We tested this possibility using our wind models. We calculated tailored wind models for stellar parameters corresponding to selected individual O stars from the Large Magellanic Cloud as derived from a previous analysis. To model the wind, we used our global wind code that calculates the radiative force from the solution of the radiative transfer equation in the comoving frame. Wind models calculated for particular stellar parameters reproduce the observational mass-loss rates better than simple scaling relations derived from model grids. This indicates that the dependence of the mass-loss rate on the other stellar parameters except the luminosity might explain part of the dispersion in the relation between the mass-loss rate and luminosity. However, some dispersion still remains, which might indicate that wind variability is another source of the dispersion.