CME activity of the Sun in different evolutionary stages

Between the Sun and the Earth there is a permanent interaction via solar radiation and the solar wind. In addition we know radiation outbreaks (flares) and mass expulsions (CMEs) which occur sporadically on the Sun. All of these permanent and sporadic phenmona make the Space Weather. Moreover, all of these phenomena determine the evolution of stars and planets. An increased stellar CME activity causes higher stellar mass and angular momentum loss which slows down the stellar rotation (stellar spin-down) and weakens the magnetic activity. Therefore CMEs influence also stellar evolution. Model calculations have shown that frequent CMEs together with a strong short-wavelength radiation environment may cause planetary atmospheric erosion or even destruction of atmospheres of close-in orbiting planets. This means that CMEs also influence planetary habitability. On the Sun flares and CMEs are relatively well investigated due to the fact that the Sun is our nearest star. In general, detecting those phenomena on other stars is more difficult. It is a well known fact that young stars exhibit stronger activity, which means stronger magnetic fields as the present-day Sun. Young stars exhibit therefore more energetic and more frequent flares. CMEs of young stars are poorly investigated. We aim for a statistical characterisation of CMEs of young solar-like stars to gain insights in the early phase of solar activity. This characterization includes determination of velocity, mass and occurrence rate of CMEs. For detecting CMEs we use the signature of moving stellar material which is the Doppler shifted emission or absorption in spectral lines. To reach these goals we use observations from the European Southern Observatory (ESO) in Chile, telescopes offered via OPTICON, and the observatory Lustbühel in Austria, as well as solar observations from the solar observatory Ondrejov in the Czech republic. With this proposal it will be for the first time possible to statistically characterize CMEs of young solar analogue stars representing the Sun in different evolutionary stages and to gain therefore insights in the CME activity of the young Sun. We can therefore for the first time determine the stellar mass loss caused by CMEs in the early phase of solar evolution.

Coronal Mass Ejections (CMEs) contribute significantly to "space weather" in the Solar System. They are responsible for the beautiful aurorae, but can also lead to power outages or damage satellites. If CMEs are energetic and occur frequently, they could cause severe atmospheric erosion on close-in orbiting exoplanets. Moreover, CMEs may have a currently unknown contribution to stellar mass- and angular momentum loss. On the Sun, this phenomenon is well investigated, but not on more distant stars. One of the possible detection methods for stellar CMEs uses signatures in optical spectra, which are far more easy to obtain compared to wavelengths which are accessible only from space. Especially for monitoring stars for longer timescales this method is the best-suited. As we are interested in the CME activity of the "Sun in time", i.e. the Sun from its birth to present, we select so-called "solar analogue" stars of different ages, resembling the Sun in different evolutionary stages. We monitored a handful of bright solar analogues for around 3 years using the institute's half-meter telescope located at the border of Graz, Austria, and analysed existing data from Pic du Midi, France, Hawaii, US, and the European Southern Observatory (ESO), Chile. We did not find any signatures of CMEs in any of these observations. To interpret these non-detections, we developed a semi-empirical model to estimate the expected number of CME signatures of all target stars. We found that many data sets (especially the archival data) were too short to detect CMEs. For the longer observations, we conclude that either massive CMEs occur less frequently than expected, or that their optical signatures are fainter than expected on these stars. The majority of optical CME detections in the literature occurred on stars smaller and cooler than the Sun, so-called "M-stars". They all appeared as emission signatures and were therefore thought to originate from erupting "prominences", i.e. CME cores seen against the dark background aside from the stellar disk (in contrast to erupting "filaments", which are the same phenomenon, but seen against the disk and seen as absorption signatures). By applying radiative transfer modeling to one previously known stellar CME, we could show that on M-stars, emission signatures can also be caused by filaments if they have higher temperatures than on the Sun. The field of stellar CME research is growing, especially during the last years the interest in this phenomenon has increased because of its numerous implications. More efforts are needed to properly identify and characterize stellar CMEs, with the goal to statistically determine their parameters, just like on the Sun.