MAGNETIC ACTIVITY OF YOUNG LATE-TYPE STARS

Abstract

Most young stars exhibit a large number of solar-like activity phenomena such as strong X-ray emission, flares, dark spots, wind, activity cycles, etc. Activity phenomena are believed to be a by-product of the nagnetic fields generated by young stars within their convective envelopes through dynamo processes. However, young stars show the existence of strong magnetic field (up to several kG), weak differential rotation, and the absence of a radiative core. All these facts challenge modern dynamo models. We review various manifestations of activity and some magnetic properties of young stars such as field strength, large-scale topology, differential rotation, and activity cycles. In particular, we point out such features of the young stars activity as the presence of vast spotted regions (up to 80% of the stellar surface), the long-term stability of the phase light curves, the absence of differential rotation (for some objects), the presence of axisymmetric and poloidal structures of the large-scale magnetic field, and some others. We then proceed to discuss the relationship between magnetic field topology, coronal X-ray emission, rotation, stellar age, and activity throughout the evolution of young stars and to compare these dependencies with the results for more evolved stars. Finally, we discuss our insight into the stellar magnetism origin and its impact on the early evolution of young convective stars.