Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 67, p. 5-14 (2023)

MAGNETO-ACTIVE LONGITUDES IN THE SUN AND STARS

Valery KRIVODUBSKIJ, DSc (Phys. & Math.)
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine


Abstract

An overview of studies of long-term increased magnetic activity in two discrete longitudinal intervals observed on the Sun and on the surface of stars of certain types is reviewed. Active longitudes on the Sun were first discovered at the end of the 19th century. Today, as a result of statistical analysis of data observed for more than a century, it has been established that there are two active longitudinal sectors on the solar surface, shifted by approximately 180° relative to each other, which can stably maintain the phase coherence of activity for a long time. At each given moment of time, one of the two longitude intervals are more active (dominant). The occasionally observed “flip-flop” phenomenon, the essence of which consists in a sudden rapid switching of the specified dominance between two active longitudes, is highlighted. The detected phenomenon is regularly repeated, which indicates the existence of stellar magnetic flip-flop cycles. At the same time, solar-type cycles are also characteristic of young analogues of the Sun. On the other hand, based on the evolution of the spot area, a magnetic flip-flop cycle with a duration of about 3.7 years was also detected on the Sun. It is relevant that the ratio of the periods of both types of cycles for young dwarfs and the Sun is the same: the flip-flop cycle is approximately 3-4 times shorter than the cycle of the solar type. That is, the structure and evolution of active longitudes on the Sun is similar to the observed active longitudes on the surface of cold stars that rotate quickly and have outer convective shells. Mechanisms of excitation of magnetically active longitudes proposed by the researchers were analyzed. Dynamo-excitation models of axially asymmetric magnetic harmonics look promising. Our calculations showed that the aW-dynamo models with the involvement of helioseismological data on the internal rotation of the Sun ensure the coexistence of dipole and quadrupole harmonics of the global magnetic field, which are necessary for the reproduction of selected longitudinal sectors of increased magnetic activity.

Key words
Magnetic activity of the Sun, sunspots, magnetic spotting of stars, “flip-flop” phenomenon, dynamo model of the magnetic cycle.

References

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