Magnetic field and potential planet candidates of the nearby Red dwarf Gliese 729

Star system: Ross 154 | Distance from the Sun: 9.7 light years

Gliese 729 (Ross 154) is the seventh closest Red dwarf to the Sun and serves as a significant subject for exoplanet research. Because Red dwarfs are typically very active, their magnetic fields can create noise that masks the subtle signals of orbiting planets. By analyzing a decade of data, the magnetic field of Gliese 729 has been mapped, revealing how its activity affects the search for small, rocky worlds in its vicinity.

The research utilized spectropolarimetric data—a technique that measures the polarization of light to reveal magnetic field structures—spanning four different time periods over 10 years. This allowed for the reconstruction of the star's large-scale magnetic field. The findings indicate that the magnetic field is relatively weak, ranging from 50 to 145 Gauss, and changes its shape over time, fluctuating between different geometric configurations.

To search for planets, the team analyzed radial velocity data, which tracks the tiny wobbles a star makes when tugged by the gravity of an orbiting planet. They used statistical modeling to account for stellar activity. While the models could not definitively confirm a planet, a repeating signal with a 7-day period and an amplitude of 1.9 meters per second was consistently identified. This signal might represent an Earth-mass or Super-Earth planet, though it could also be an artifact of the star's internal magnetic activity.

Key findings
- Gliese 729 exhibits a weak, evolving large-scale magnetic field ranging from 50 to 145 Gauss.
- Magnetic field geometry shifts between poloidal (north-south) and complex toroidal configurations.
- A 7-day period signal was detected in radial velocity data, which could indicate a low-mass planet or stellar noise.
- The results highlight the difficulty of distinguishing between planetary gravitational signals and magnetic activity in active Red dwarfs.

Scientific study

RedDots: Magnetic field of the nearby active M dwarf GJ 729, and a search for companions (external link)