Spectropolarimetry reveals weak magnetic field in Maunder Minimum-like star HD 166620

Star system: HD 166620 | Distance from the Sun: 36.2 light years

HD 166620 is a star thought to be in a Maunder Minimum-like state, a period of very low magnetic activity similar to what the Sun experienced in the 17th century. Using spectropolarimetric observations from the CFHT/SPIRou and ESPaDOnS instruments, astronomers analyzed the star’s magnetic field over 12 nights. While individual measurements showed no strong polarization, combining the data revealed a weak, axisymmetric dipole field with a strength of about 1.1 Gauss, matching predictions for the Sun during its Maunder Minimum.

The results are consistent with other independent measurements and rule out the presence of strong, complex magnetic fields. This provides direct evidence that stars in a Maunder Minimum-like state have weakened large-scale magnetic fields, leading to reduced magnetic braking—the process that slows a star’s rotation over time. HD 166620 thus serves as an important example of how stellar magnetic activity can change and affect stellar evolution.

Key findings
- HD 166620 shows a weak, axisymmetric dipole magnetic field of about 1.1 Gauss
- The field strength matches predictions for the Sun during the Maunder Minimum
- No evidence for strong, complex magnetic fields was found
- The results support the idea that weakened magnetic braking is linked to reduced large-scale magnetic fields
- HD 166620 is a valuable analog for studying the Sun’s past and stellar evolution

Scientific study

Spectropolarimetric Constraints on the Maunder Minimum Analog HD 166620: Evidence for Weakened Magnetic Braking (external link)