Context. WR104 is an emblematic dusty Wolf-Rayet star and the prototypical member of a sub-group hosting spirals that are mainly observable with high-angular resolution techniques. Previous aperture masking observations showed that WR104 is likely to be an interacting binary star at the end of its life. However, several aspects of the system are still unknown. This includes the opening angle of the spiral, the dust formation locus, and the link between the central binary star and a candidate companion star detected with the Hubble Space Telescope (HST) at 1′′. Aims. Our aim was to directly image the dusty spiral or “pinwheel” structure around WR104 for the first time and determine its physical properties at large spatial scales. We also wanted to address the characteristics of the candidate companion detected by the HST. Methods. For this purpose, we used SPHERE and VISIR at the Very Large Telescope to image the system in the near- and mid-infrared, respectively. Both instruments furnished an excellent view of the system at the highest angular resolution a single, ground-based telescope can provide. Based on these direct images, we then used analytical and radiative transfer models to determine several physical properties of the system. Results. Employing a different technique than previously used, our new images have allowed us to confirm the presence of the dust pinwheel around the central star. We have also detected up to five revolutions of the spiral pattern of WR104 in the K band for the first time. The circumstellar dust extends up to 2 arcsec from the central binary star in the N band, corresponding to the past 20 yr of mass loss. Moreover, we found no clear evidence of a shadow of the first spiral coil onto the subsequent ones, which likely points to a dusty environment less massive than inferred in previous studies. We have also confirmed that the stellar candidate companion previously detected by the HST is gravitationally bound to WR104 and herein provide information about its nature and orbital elements.

The recent discovery of a spectacular dust plume in the system 2XMM J160050.7–514245 (referred to as ‘Apep’) suggested a physical origin in a colliding-wind binary by way of the ‘Pinwheel’ mechanism. Observational data pointed to a hierarchical triple-star system, however, several extreme and unexpected physical properties seem to defy the established physics of such objects. Most notably, a stark discrepancy was found in the observed outflow speed of the gas as measured spectroscopically in the line-of-sight direction compared to the proper motion expansion of the dust in the sky plane. This enigmatic behaviour arises at the wind base within the central Wolf–Rayet binary: a system that has so far remained spatially unresolved. Here, we present an updated proper motion study deriving the expansion speed of Apep’s dust plume over a 2-year baseline that is four times slower than the spectroscopic wind speed, confirming and strengthening the previous finding. We also present the results from high angular resolution near-infrared imaging studies of the heart of the system, revealing a close binary with properties matching a Wolf–Rayet colliding-wind system. Based on these new observational constraints, an improved geometric model is presented yielding a close match to the data, constraining the orbital parameters of the Wolf–Rayet binary and lending further support to the anisotropic wind model.

The Wolf–Rayet (WR) binary system WR140 is a close (0.9–16.7 mas; ref. 1) binary star consisting of an O5 primary and WC7 companion2 and is known as the archetype of episodic dust-producing WRs. Dust in WR binaries is known to form in a confined stream originating from the collision of the two stellar winds, with orbital motion of the binary sculpting the large-scale dust structure into arcs as dust is swept radially outwards. It is understood that sensitive conditions required for dust production in WR140 are only met around periastron when the two stars are sufficiently close2–4. Here we present multiepoch imagery of the circumstellar dust shell of WR140. We constructed geometric models that closely trace the expansion of the intricately structured dust plume, showing that complex effects induced by orbital modulation may result in a ‘Goldilocks zone’ for dust production. We find that the expansion of the dust plume cannot be reproduced under the assumption of a simple uniform-speed outflow, finding instead the dust to be accelerating. This constitutes a direct kinematic record of dust motion under acceleration by radiation pressure and further highlights the complexity of the physical conditions in colliding-wind binaries.