An extensive spectroscopic time series of three Wolf–Rayet stars – I. The lifetime of large-scale structures in the wind of WR 134

Abstract

During the summer of 2013, a 4-month spectroscopic campaign took place to\nobserve the variabilities in three Wolf-Rayet stars. The spectroscopic data\nhave been analyzed for WR 134 (WN6b), to better understand its behaviour and\nlong-term periodicity, which we interpret as arising from corotating\ninteraction regions (CIRs) in the wind. By analyzing the variability of the He\nII $\\lambda$5411 emission line, the previously identified period was refined to\nP = 2.255 $\\pm$ 0.008 (s.d.) days. The coherency time of the variability, which\nwe associate with the lifetime of the CIRs in the wind, was deduced to be 40\n$\\pm$ 6 days, or $\\sim$ 18 cycles, by cross-correlating the variability\npatterns as a function of time. When comparing the phased observational\ngrayscale difference images with theoretical grayscales previously calculated\nfrom models including CIRs in an optically thin stellar wind, we find that two\nCIRs were likely present. A separation in longitude of $\\Delta \\phi \\simeq$\n90$^{\\circ}$ was determined between the two CIRs and we suggest that the\ndifferent maximum velocities that they reach indicate that they emerge from\ndifferent latitudes. We have also been able to detect observational signatures\nof the CIRs in other spectral lines (C IV $\\lambda\\lambda$5802,5812 and He I\n$\\lambda$5876). Furthermore, a DAC was found to be present simultaneously with\nthe CIR signatures detected in the He I $\\lambda$5876 emission line which is\nconsistent with the proposed geometry of the large-scale structures in the\nwind. Small-scale structures also show a presence in the wind, simultaneously\nwith the larger scale structures, showing that they do in fact co-exist.\n