Magnetic activity cycles found in exoplanet-hosting red dwarf stars Gliese 617 A and Lalande 21185

Star system: Lalande 21185 | Distance from the Sun: 8.3 light years

M dwarf stars are small, cool stars that are popular targets for finding exoplanets because their size makes it easier to detect planets in their habitable zones. However, these stars often have magnetic activity that can mimic the signals of planets, making it important to understand their activity cycles. This study focused on two M dwarfs, Gliese 617 A and Lalande 21185 (Gliese 411), both known to host exoplanets.

Researchers analyzed 13 years of high-resolution spectra from the SOPHIE spectrograph, monitoring the stars' magnetic activity using two different indicators. They found a magnetic activity cycle of about 4.8 years in Gliese 617 A and several cycles around 4.9 years in Lalande 21185. These cycles do not match the periods of any known planets around these stars, suggesting the signals are truly due to magnetic activity and not planets.

The study also found that the magnetic cycles in these two stars may be caused by different mechanisms. Gliese 617 A's cycle is similar to the Sun's, while Lalande 21185's cycle seems to be influenced by the star's rotation. Understanding these cycles helps astronomers avoid confusing stellar activity with planet signals when searching for new worlds.

Key findings
- Magnetic activity cycles of about 4.8–4.9 years were found in M dwarfs Gliese 617 A and Lalande 21185.
- The cycles are not related to the planets orbiting these stars, confirming their magnetic origin.
- The mechanisms driving the cycles may differ between the two stars, with one resembling the Sun's cycle and the other influenced by rotation.

Scientific study

Long-term activity cycles in planetary M stars observed with SOPHIE (external link)