Work

What powers the most energetic flares in the field? Kepler. Revisiting the superflaring star KIC 2852961

Year: 2026

Type: article

Abstract: Flare activity in red giants, once thought to be extremely rare, is actually quite common when continuously monitored with high-precision space photometry. In fact, the most powerful flares, also known as 'superflares', with bolometric energies exceeding 10 38 ,erg have been observed on red giant stars. KIC,2852961 is a red giant star producing the highest-energy flares in the Kepler field, and is also known for its large-amplitude starspot-induced light variations. Our goal is to find out what causes the extreme flare activity and flare energies in this star. For our investigations, we use ground-based spectroscopic measurements and space photometric data, which we process using standard tools. We also collect relevant data from databases of large surveys such as . Gaia Our new radial velocity data confirm that the red giant star is part of a close binary system, in which tidal forces play a crucial role in controlling the evolution of the binary system. Our results show that tidal evolution has driven the system close to orbital circularization and rotational synchronization, but it did not completely constrain the differential rotation of the red giant, in which the magnetic dynamo can operate extremely efficiently. We find that high-energy (super)flares are primarily controlled by the internal magnetic activity of the active giant component, rather than phase-dependent interactions with the secondary star. The large spot-induced rotational light modulations indicate extensive starspots that can store enormous amounts of magnetic energy. This provides the conditions for the formation of extremely large flares, confirming the close relationship between large spot coverage and high flare energies and/or frequency. Behind all this, differential rotation may play a dual role in the flare activity of KIC,2852961: it contributes both to the formation of large starspots and to the shearing and twisting of coronal magnetic fields that can power energetic superflares.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202662757