SeStCoOs · Seismology of Stellar Coronal Oscillations

Seismology of Stellar Coronal Oscillations

Many low-mass stars are surrounded by a stellar corona, which can be observed with X-ray emission. These coronae regularly show flares, as is also observed for the corona of the sun. These flares often exhibit oscillatory patterns. The project SeStCoOs was aimed at performing seismology of such stellar coronal oscillations. This would be achieved by a two-pronged attack: on the one hand Aim 1 set out to perform forward modelling (creating artificial observations of the oscillations), while Aim 2 was targeting the observational aspects in order to directly detect the stellar flare oscillations and perform seismology. In Aim 1, we have accomplished all goals of the project. Before the project started, a numerical code (FoMo, http://wiki.esat.kuleuven.be/FoMo) was constructed to perform forward modelling of coronal oscillations. This code has been used to perform forward modelling of compressive oscillations in stellar coronae (EUV emission: Antolin & Van Doorsselaere 2013, De Moortel et al. 2014, radio emission: Reznikova et al. 2014, Reznikova et al. 2015) and of transverse oscillations (Antolin et al. 2014). It was shown that these transverse oscillations may lead to the generation of strand-like structures in the solar corona, where they are often observed in high-resolution observations. There are ongoing efforts to improve the models, in particular the emission of curved transversely oscillating loops is being analysed by Dr. Victor Melnikov (Pulkovo) who was a visitor under the ERGrant. The data for this project were generated by Stief Gijsen, a PhD student partly paid by this project. We have extended Aim 1 to also model photospheric oscillations in magnetic pores and sunspots. This was mainly undertaken by a PhD student Michael Moreels who was partly hired on this project. We have created analytical and numerical models for the prediction of phase differences between magnetic field, surface area, intensity and Doppler velocity oscillations for such waves. We have used these models to design data analysis methods that can accurately determine the structure of the magnetic pore. Aim 2 was focussed on the observational aspects of the seismology of stellar coronal oscillations. To that end, we have studied oscillations in the stellar megaflare reported by Kowalski et al. (2010). The results of that observational study have been reported in Anfinogentov et al. (2013), where we show that the observed oscillations are most likely compressive slow oscillations. The seismological values for the lengths of flaring loops is compatible with direct modelling. During the project, additional funds were obtained to organise a workshop on Seismology of Stellar Coronal Oscillations at the Lorentz Centre (Leiden, The Netherlands). This small scale workshop was by invitation only, and gathered world renowned experts in stellar flares and their oscillations. This workshop lead directly to an ongoing collaboration with L. Balona on the observations of flares (and their oscillations) in the Kepler observations. Moreover, research is ongoing on the interpration of stellar flare oscillations on AF Psc, in collaboration with Gerry Doyle (Armagh Observatory). Also, the results from Aim 1 have been and are currently being used for the seismology of compressive waves in magnetic pores and sunspots, and the energy flux they contain. This project is being lead by Michael Moreels and is in collaboration with the University of Sheffield and Queen's University Belfast. Several papers have been submitted to international journals.

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