Prof. YAN Xiaoli and the collaborators from Yunnan Observatories of the Chinese Academy of Sciences (CAS) found magnetic structure conversion and material transfer in a failed solar filament eruption. The study was published online in The Astrophysical Journal.

Solar filaments/prominences suspended in the solar corona are large-scale magnetic structures with relatively cool and dense materials. Their density is 100 times higher and temperature is 100 times lower than those of the surrounding environment. According to the locations of solar filaments, they are classified into quiescent filaments, active-region filaments, and intermediate filaments.

To obtain the exact magnetic structures and the detailed eruption process, the researchers studied a failed solar active-region filament eruption associated with a C-class flare by using high-resolution H-alpha images from the New Vacuum Solar Telescope (NVST), and the EUV and vector magnetic field observations from the Solar Dynamical Observatory (SDO).

Active region is one of the important observational targets for solar telescope as solar eruptions often occur in active region on the Sun. When NOAA active region 12740 with the α-type configuration first appeared at the east solar limb on May 5, 2019, the NVST began to observe it. The magnetic configuration became βδ-type on May 6, 2019. The eruptive activities also became frequent. On May 7, 2019, the NVST observed the eruptions of two S-shaped active-region filaments occurring this active region.

After analyzing the multi-wavelength observations, the researchers found that one filament (labeled as F2) was first disturbed by another filament (labeled as F1) eruption that experienced a whip-like motion.

Using the constructed Dopplergrams, they found that the southern and the northern parts of the filament F2 body exhibit simultaneously blueshift and redshift along the filament spine before its eruption. The filament F2 was experiencing a rolling motion from one side to the other. During the filament F2 eruption, the Dopplergrams of the filament body exhibited an opposite sign comparing with those before its eruption. That is to say, the filament body experienced an untwisting motion, which can also be identified by tracing the movement of the eruptive filament threads.

Moreover, the material of the filament F2 was transferred to the surrounding magnetic field loops during its eruption, which is caused by magnetic reconnection between the magnetic structure of the filament F2 and the surrounding magnetic loops. According to the right-bearing threads of the filament F2 before its eruption, it can be deduced that the magnetic structure of the filament F2 is a sheared arcade. However, the obvious untwisting motion was found during its eruption. Therefore, the only explanation is that the twisted magnetic structure of filament F2 formed in the eruption phase.

This study reveals that when the twisted structure of the filament formed and why the filament experienced a failed eruption. The results are important for understanding the detailed process of the filament eruption and forecasting solar eruptions.

Solar filament eruptions are usually associated with solar flares and coronal mass ejections (CMEs), thus, the research about solar filament become one of the important issues in solar research field.