Detection of high-frequency pulsation in WR 135: investigation of stellar wind dynamics

TL;DR

This study detects high-frequency pulsations in WR 135 through optical photometry and spectroscopy, revealing stratified wind dynamics and pulsation-driven clumping in the star's stellar wind.

Contribution

It is the first to identify high-order harmonic pulsations in WR 135 and links these to wind stratification and clump formation using radiative transfer modeling.

Findings

Detection of harmonics up to 6th order in photometry

Weaker 8th harmonic detected in emission lines

Wind stratification driven by different opacities and pulsations

Abstract

We report the detection of high-frequency pulsations in WR\,135 from short cadence (10\,minutes) optical photometric and spectroscopic time series surveys. The harmonics up to $6^{th}$ order are detected from the integrated photometric flux variations while the comparatively weaker $8^{th}$ harmonic is detected from the strengths of the emission lines. We investigate the driving source of the stratified winds of WR\,135 using the radiative transfer modeling code, CMFGEN, and find the physical conditions that can explain the propagation of such pulsations. From our study, we find that the optically thick sub-sonic layers of the atmosphere are close to the Eddington limit and are launched by the Fe-opacity. The outer optically thin super-sonic winds ($\tau_{ross}=0.1-0.01$) are launched by the He\,$\textsc{ii}$ and C\,$\textsc{iv}$ opacities. The stratified winds above the sonic point undergo velocity perturbation that can lead to clumps. In the optically thin supersonic winds, dense clumps of smaller size ($f_{VFF}=0.27-0.3$, where $f_{VFF}$ is the volume filling factor) pulsate with higher-order harmonics. The larger clumps ($f_{VFF}=0.2$) oscillate with lower-order harmonics of the pulsation and affect the overall wind variability.