Constraining stellar CMEs by solar observations

The Sun exhibits solar storms called coronal mass ejections (CMEs). These are magnetized plasma clouds which are ejected from the Sun and driven by magnetic energy. When directed towards the Earth, they may interact with the Earths magnetic field and cause beautiful aurorae but are sometimes so powerful that they can damage satellites and may also lead to power outages on Earth. Such storms are also known from other stars, and modeling results have shown that if a planet orbiting a star which generates such storms has no magnetic field, then the planet may lose its atmosphere. As a planetary atmosphere is a requirement for the origin and development of life, it is important to know more about stellar CMEs to evaluate if an exoplanetary world may be capable of hosting life or not. Up to now, only a handful of distinct stellar CMEs is known and the methods to detect them are manifold. Optical spectroscopic observations have yielded so far the largest number of candidate CME events. For this method, optical spectroscopic time series need to be obtained which was done quite heavily in the recent past. When a CME erupts from a star or the Sun, this leaves a signature in an optical spectrum which is related to the mass and the speed of the erupted CME. However also other phenomena can cause similar signatures, e.g. plasma flows in magnetic loops on the Sun connected with an outbreak of radiation, a so-called flare, a phenomenon which is spatially and temporally correlated with CMEs. On stars one can not directly image a CME as on the Sun. Therefore we propose in the project to use solar optical spectroscopic observations of flares and CMEs obtained by the MEES solar observatory, on Hawaii which has captured solar storms over a period of 15 years. For solar CMEs we can derive their optical spectroscopic signatures, which we measure also on stars, but we see at the same time which phenomenon causes these signatures due to the fact that we are able to spatially resolve phenomena on these Sun, which is not feasible for stars. By doing so we are able to improve the understanding of optical signatures of CMEs and can therefore much better interpret the numerous stellar CME candidate events presented so far in the literature. Additionally we also involve solar ultraviolet observations from UVCS onboard the space observatory SOHO, as UVCS has observed solar CMEs at different heights compared to the MEES observations. With both optical and UV observations we can also get information on the propagation of solar CMEs, as both data have been obtained at different heights on the Sun. With the approach of combining solar and stellar observations we aim for a much better understanding of the identification and characterization of stellar storms.