Stellar magnetic fields are changing!
An international study involving the Montpellier University and Particles Laboratory (UM – CNRS) has just shown that the magnetic field of the red dwarf star AD Leonis is undergoing a reversal of polarities, a first for this type of star. These results, published in the journal Astronomy and Astrophysics, were obtained thanks to 15 years of observations with the Canada-France-Hawaii Telescope and the Bernard Lyot Telescope.
The 11-year solar activity cycle is a well-known phenomenon, during which the intensity of the Sun's magnetic field varies and its polarities reverse. Over the past 30 years, astronomers have identified similar behavior in several stars similar to the Sun. But until now, no magnetic polarity reversal has been observed in their cooler counterparts, red dwarf stars.
An international team including scientists from IRAP, LUPM, IPAG, IAP, and LAM has just shown that the magnetic field of the notoriously active red dwarf AD Leonis could be approaching a polarity reversal, based on observations spanning 15 years. These data were obtained using the ESPaDOnS and SPIRou instruments at the Canada-France-Hawaii Telescope (CFHT) and NARVAL at the Bernard Lyot Telescope (TBL).
AD Leonis is a notoriously active red dwarf star with a magnetic field approximately 1,000 times stronger than that of the Sun. More generally, the magnetic fields of red dwarfs differ greatly from the solar magnetic field, and it is not yet known whether they can exhibit magnetic cycles, although there are indications of activity cycles.
Red dwarf stars and exoplanets
AD Leonis was regularly observed between 2019 and 2020 using the SPIRou instrument as part of the Legacy Survey. The study conducted by Stefano Bellotti, a doctoral student at IRAP, shows that not only has the intensity of the magnetic field been decreasing continuously since observations began in 2006 with the ESPaDOnS and NARVAL instruments, but also that the star's magnetic poles have begun to flip. Although no polarity reversal occurred during the SPIRou observations, these results indicate that red dwarfs such as AD Leonis may undergo magnetic cycles, like the Sun. This encourages astronomers to continue observing AD Leonis for several more years.
This result provides a better understanding of how magnetic fields are generated in stars that are cooler than the Sun. Furthermore, studying the magnetic fields of red dwarfs—prime targets for detecting Earth-like rocky exoplanets—such as AD Leonis is essential for understanding the space environment in which rocky exoplanets orbit. This is because a star's magnetic field regulates the space weather in its vicinity, namely the energetic phenomena associated with stellar activity—such as flares and coronal mass ejections—which play a critical role in an exoplanet's ability to maintain an atmosphere during its evolution and thus remain habitable.
Find the study Monitoring the large-scale magnetic field of AD Leo with SPIRou, ESPaDOnS, and Narval