Revealing the Accelerating Wind in the Inner Region of Colliding-wind Binary WR 112

Abstract Colliding winds in massive binaries generate X-ray-bright shocks, synchrotron radio emission, and sometimes even dusty “pinwheel” spirals. We report the first X-ray detections of the dusty WC+O binary system WR 112 from Chandra and Swift, alongside 27 yr of Very Large Array/Australia Telescope Compact Array radio monitoring and new diffraction-limited Keck images. Because we view the nearly circular orbit almost edge-on, the colliding-wind zone alternates between heavy Wolf–Rayet wind self-absorption and near-transparent O-star wind foreground each 20 yr orbit, producing phase-locked radio and X-ray variability. This scenario leads to a prediction that the radio spectral index is flatter from a larger nonthermal contribution around the radio intensity maximum, which indeed was observed. Existing models that assume a single dust-expansion speed fail to reproduce the combined infrared (IR) geometry and radio light curve. Instead, we require an accelerating postshock flow that climbs from near-stationary to ∼1350 km s −1 in about one orbital cycle, naturally matching the IR spiral from 5″ down to within 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>″</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 1, while also fitting the phase of the radio brightening. These kinematic constraints supply critical boundary conditions for future hydrodynamic simulations, which can link hot-plasma cooling, nonthermal radio emission, X-ray spectra, and dust formation in a self-consistent framework. WR 112 thus joins WR 140, WR 104, and WR 70-16 (Apep) as a benchmark system for testing colliding-wind physics under an increasingly diverse range of orbital architectures and physical conditions.

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Journal
The Astronomical Journal
Published
2025-09-12
DOI
https://doi.org/10.3847/1538-3881/adfa03
Citations
1
Primary Topic
Astrophysical Phenomena and Observations
Type
article
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article

Revealing the Accelerating Wind in the Inner Region of Colliding-wind Binary WR 112

A. Soulain, P. G. Edwards, John D. Monnier, J. R. Callingham et al.
1 citations
The Astronomical Journal
Astrophysical Phenomena and Observations
1.15
article

Revealing the Accelerating Wind in the Inner Region of Colliding-wind Binary WR 112

A. Soulain, P. G. Edwards, John D. Monnier, J. R. Callingham, Christopher M. P. Russell, Peter Tuthill, P. M. Williams, J. M. Mïller, M. F. Corcoran, Kenji Hamaguchi, Ryan M. Lau, Yinuo Han, A. F. J. Moffat, Samaporn Tinyanont, W. C. Danchi, Garreth Ruane, L. J. Greenhill, M. Hankins, Sanne Bloot, Jason Wang
article en
1 citations

Abstract

Abstract Colliding winds in massive binaries generate X-ray-bright shocks, synchrotron radio emission, and sometimes even dusty “pinwheel” spirals. We report the first X-ray detections of the dusty WC+O binary system WR 112 from Chandra and Swift, alongside 27 yr of Very Large Array/Australia Telescope Compact Array radio monitoring and new diffraction-limited Keck images. Because we view the nearly circular orbit almost edge-on, the colliding-wind zone alternates between heavy Wolf–Rayet wind self-absorption and near-transparent O-star wind foreground each 20 yr orbit, producing phase-locked radio and X-ray variability. This scenario leads to a prediction that the radio spectral index is flatter from a larger nonthermal contribution around the radio intensity maximum, which indeed was observed. Existing models that assume a single dust-expansion speed fail to reproduce the combined infrared (IR) geometry and radio light curve. Instead, we require an accelerating postshock flow that climbs from near-stationary to ∼1350 km s −1 in about one orbital cycle, naturally matching the IR spiral from 5″ down to within 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>″</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 1, while also fitting the phase of the radio brightening. These kinematic constraints supply critical boundary conditions for future hydrodynamic simulations, which can link hot-plasma cooling, nonthermal radio emission, X-ray spectra, and dust formation in a self-consistent framework. WR 112 thus joins WR 140, WR 104, and WR 70-16 (Apep) as a benchmark system for testing colliding-wind physics under an increasingly diverse range of orbital architectures and physical conditions.

The Astronomical JournalVol. 170(4)
Northwestern University (US), California Institute of Technology (US), Commonwealth Scientific and Industrial Research Organisation (AU), Centre National de la Recherche Scientifique (FR), The University of Sydney (AU), Australia Telescope National Facility (AU), Goddard Space Flight Center (US), Jet Propulsion Laboratory (US), Université du Québec à Montréal (CA), University of America (US), University of Groningen (NL), University of Michigan (US), Royal Observatory (GB), Center for Astrophysics Harvard & Smithsonian (US), Astrophysics Science Division (US), Community Science and Data Center (US), Astronomy Australia (AU), NSF NOIRLab (US), Université de Montréal (CA), University of Maryland, Baltimore County (US), Catholic University of America (US), National Astronomical Research Institute of Thailand (TH), University of Delaware (US), University of Amsterdam (NL), Université Grenoble Alpes (FR), Netherlands Institute for Radio Astronomy (NL), Arkansas Tech University (US), University of Edinburgh (GB)
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Astrophysical Phenomena and Observations
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