Studying the stellar surface structure and magnetic cycles in very active stars using Doppler imaging and long-term photometric observations
Final Report Abstract
In this project we investigated the enigmatic flip-flop phenomenon in which the stellar magnetic activity concentrates on two active longitudes 180° apart, and every few years periodically changes the active longitude. In the framework of this project theoretical modelling of the flip-flop phenomenon using solar-like rotation law, weak differential rotation and anisotropic a-effect was carried out. These models can produce the general characteristics of the flip-flop phenomenon, but according to our calculations, the shift of the spots in a flip-flop event is 180° only in some cases, and then mainly for the stars with thin convective zones. In stars with thick convective zones we found a shift that is close to 90°. The model calculations were also converted into synthetic photometric observations. This was used to investigate the expected long-term photometric behaviour of active stars showing the flip-flop phenomenon. The results showed that the flip-flop phenomenon is characterised by alternating periods of large and small light-curve amplitudes. This information is used in the search for new stars exhibiting this intriguing phenomenon Another focus in this study was to investigate the flip-flop phenomenon in young stars. Long-term photometric observations of three young solar-like stars, AB Dor, EK Dra and V889 Her, were investigated. From these stars EK Dra is the best analogue known for the young Sun. All these stars show flip-flops, and in AB Dor and EK Dra the events are periodic, with cycle lengths of 5.5 and 4.5 years, respectively. The more detailed study of the spot configurations using Doppler imaging techniques confirmed the findings of the lower resolution photometric study.
Publications
- Flip-flop phenomenon: observations and theory, 2005, AN 326,278
Elstner D., Korhonen H.
- Magnetic activity in the young solar analog AB Dor - Active longitudes and cycles from long-term photometry, 2005, A&A, 432, 657
Järvinen S.P., Berdyugina S.V., Tuominen L, Cutispoto G., Bös M.
- Photometric observations from theoretical flip-flop models, 2005, A&A 440, 1161
Korhonen H., Elstner D.
- Spot activity cycles and flip-flops on young solar analogs, 2005, AN 326, 283
Berdyugina S.V., Järvinen S.P.
- Spots on EK Draconis - Active longitudes and cycles from long-term photometry, 2005, A&A, 440, 735
Järvinen S.P., Berdyugina S.V., Strassmeier K.G.
- Study of FK Comae Berenices VI. Time-series photometric modelling and a flip-flop in real time, 2006, A&A 452, 303
Oláh K., Korhonen H., Kovári Zs., Forgács-Dajka E., Strassmeier K.G.
- The Remarkable Far-Ultraviolet Spectrum of FK Comae Berenices: King of Spin, 2006, ApJ 644, 464
Ayres T.R., Harper G.M., Brown A., Korhonen H., Ilyin I.V., Redfield S., Wood B.E.
- EK Draconis: Magnetic activity in the photosphere and chromosphere, 2007, A&A, 472, 887
Järvinen S.P., Berdyugina S.V., Korhonen H., Ilyin I., Tuominen L.
- Study of FK Comae Berenices; V The surface differential rotation, 2007, A&A, 476, 881
Korhonen H., Berdyugina S.V., Hackman T., Ilyin I., Strassmeier K.G., Tuominen I.
- X-Ray Spectroscopic Signatures of the Extended Corona of FK Comae, 2008, ApJ, 679, 1522
Drake J.J., Chung S.M., Kashyap V, Korhonen H., Van Ballegooijen A., Elstner D.
