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arXiv · 2610.14348

Mapping Wolf-Rayet winds with spectro-interferometry I. Detection of multiple co-rotating interaction regions in WR 6

K. Deshmukh·A. -N. Chené·A. J. Frost·T. De Prins·L. Fabiani·H. Sana·R. R. Lefever·A. Mérand·N. D. Richardson·A. A. C. Sander·T. Shenar
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Abstract

WR 6 is the prototype for periodic variability due to large-scale wind structures in Wolf-Rayet (WR) stars, showing a consistent periodicity of 3.76 d in photometry, spectroscopy, and polarimetry. However, the origin of this variability is debated, attributed either to corotating interaction regions (CIRs) or a low-mass companion. We use time-resolved interferometry to investigate the origin of periodic variability in WR 6. We aim to detect and characterize structures in the stellar winds of WR 6 and discriminate between the CIR and low-mass companion scenarios. Using the extended configuration of the Auxiliary Telescopes at VLTI, we obtained six GRAVITY epochs over six months to search for the presence and variability of wind-structures in WR 6. We also obtained complementary spectroscopic observations during one of the epochs to monitor contemporaneous spectral line variability. For all six epochs of GRAVITY observations: (i) WR 6 is consistent with a single star and has no spatially resolved companion detected above $M\gtrsim6\,M_\odot$; (ii) The He I line-emitting region is spatially resolved, while the He II lines remain unresolved, consistent with atmosphere models; (iii) Around 2.19 $μ$m, discrete line-emitting features offset from the center of the star are detected. The number, positions, and wavelengths of these features vary across epochs. Spectroscopic monitoring reveals spectral line residuals that broadly correspond to the two features seen in the GRAVITY data of the fifth epoch. Finally, the first three epochs, observed on three consecutive nights, show significant variability in these features but cannot be directly linked across epochs. We thus report the detection of multiple large-scale structures in the wind of WR 6 with VLTI/GRAVITY. We favor CIRs as their likely origin owing to temporal and spatial variability that cannot be reconciled with a low-mass companion.

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K. Deshmukh, A. -N. Chené, A. J. Frost, T. De Prins, L. Fabiani, H. Sana, R. R. Lefever, A. Mérand, N. D. Richardson, A. A. C. Sander, T. Shenar. 2026-10-09. Mapping Wolf-Rayet winds with spectro-interferometry I. Detection of multiple co-rotating interaction regions in WR 6. https://arxiv.org/abs/2610.14348

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