Astronomy Tea Talk

The high energy radiation emitted by young stars can have a strong impact on their subsequent rotational evolution at later stages. This is because XEUV-driven photoevaporation is one of the major drivers of the dispersal of circumstellar disks, which surround all newly born stars during the first few million years of their evolution. Since the photoevaporative mass loss is mainly a function of stellar X-ray luminosity, the lifetimes of planet-forming disks are primarily set by the X-ray emission of their central star. Stellar rotation and X-ray activity are therefore tightly coupled, as the disk prevents the star from spinning up as it contracts through the disk-locking phase. Using a magnetic morphology-driven stellar spin-down model, we show that the disk-locking phase has a profound impact on the subsequent rotational evolution of young stars, which ultimately governs the amount of high-energy radiation received by newly formed planets. By assuming that the lifetimes of planet-forming disks are mainly determined by the X-ray luminosity of their central stars at young stages, we find that the bimodal rotation period distribution of a number of older open clusters, such as Pleiades or Praesepe, can be successfully recovered. Further we show how this model can be utilised to model the long-term evolution of the stellar high-energy irradiation that young exoplanets and their atmospheres are subject to.