No radio polarization detected in colliding-wind binaries WR 147 and HD 167971

Star system: HD 167971 A | Distance from the Sun: 4485 light years

WR 147 and HD 167971 are massive star systems where strong stellar winds collide, accelerating particles to high energies. These systems, known as particle-accelerating colliding-wind binaries (PACWBs), are expected to produce synchrotron radiation in the radio range, which should be linearly polarized. However, no such polarization has been detected so far. In this study, astronomers used the Very Large Array radio telescope to observe both systems at frequencies where synchrotron emission is strongest. They carefully calibrated the data and analyzed the polarization maps but found no evidence of linear polarization in either system.

The most conservative upper limit on the polarization degree is about one percent for both WR 147 and HD 167971. The lack of detected polarization is likely due to several factors, including turbulent magnetic fields, depolarization from Faraday rotation, and the complex geometry of the emission regions, which are not resolved by the telescope. Additionally, thermal emission from the strong stellar winds can dilute the synchrotron signal, making polarization even harder to detect. These results highlight the challenges of observing polarization in PACWBs and suggest that more sensitive observations or higher resolution may be needed in the future.

Key findings
- No linear polarization detected in WR 147 and HD 167971 at radio frequencies.
- Upper limit on polarization degree is about one percent.
- Turbulent magnetic fields, Faraday rotation, and beam depolarization likely cause the lack of signal.
- Thermal emission from stellar winds dilutes the synchrotron polarization.
- Future studies may require higher sensitivity or resolution to detect polarization.

Scientific study

Search for radio polarization in the particle-accelerating colliding-wind binaries WR 147 and HD 167971 (external link)