Abstract (eng)
By observing and studying solar-like but young stars, we can learn about the young Sun and how our solar system formed. Those young stars, only about a million years old, are very active and are still surrounded by gas and dust. Out of this circumstellar material a rotating disk forms which eventually becomes the birthplace of a planetary system.
Compared to the contemporary Sun, young stars are in an active phase of their evolution. They show up to 10 000 times stronger X-ray emission and possibly also an enhanced production of stellar energetic particles (SP). Young stars still acquire mass via accretion of circumstellar material. In this process, they experience short periods of strongly enhanced mass accretion rates causing a significant increase of the object’s luminosity. We study the impact of such energetic processes on the chemistry of the circumstellar material by using numerical simulations. We aim to identify observational tracers to constrain and to better understand the physical properties of young stars.
Our models show that the presence of a typical cluster X-ray background field has only little impact on the chemistry of protoplanetary disks. Enhanced SP fluxes, as expected for young stars, have a significant impact on disk ionization tracers. To constrain the particle flux, spatially resolved molecular ion observations and detailed modelling is required. The impact of luminosity bursts manifests in spectral line images as observable ring and X-shaped emission patterns. Based on our results, we propose a model-independent method to identify post-burst targets directly from observations.