Estimating rotation periods and magnetic cycle lengths of active stars - PhD thesis by Nigul Olspert

November 08, 2018

Nigul Olspert, M.Sc., will defend the dissertation "From periodic to cyclic processes in stellar magnetic activity research: time series analysis methods and their applications" on Friday 16 November at 12 noon at the Aalto University School of Science, lecture hall AS1, Maarintie 8, Espoo. 

In this dissertation we introduce and develop time series analysis methods which are dedicated to period and cycle length estimation of magnetically active stars. Knowing both of these quantities is important as it makes observable reality comparable with predictions from the dynamo theory. Magnetic activity is primarily manifested through dark spots on the surface of the star. However, the rotation of the star is not uniform, but differential, which makes the period estimation not a trivial task. Furthermore, over time the number of spots changes, forming a cyclic process. For instance, for the Sun the activity cycle is known to last approximately 11 years, while both the length of each individual cycle as well as the amplitude is varying. Such a behaviour is called quasi-periodic. 

Opponent: Professor Ivan Andronov, Odessa National Maritime University, Ukraine

Kustos: Aki Vehtari, Aalto University School of Science, Department of Computer Science 

Supervisors: Maarit Käpylä (Max Planck Institute for Soar System Research) and Jaan Pelt (Tartu Observatory)

Read the full Aalto University press release.

Download and read the thesis here.

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