2025 PDG seminars

Sun-as-a-star flare observations with high-resolution telescopes

Stellar flares cannot be spatially resolved, meaning we have to extract complex three-dimensional behavior from a one-dimensional disk-integrated spectral timeseries. Due to their proximity to Earth, solar flares can serve as a stepping stone for understanding their stellar counterparts, especially when using a Sun-as-a-star instrument in combination with spatially resolved observations including some large IRIS flares. In this talk, I will discuss how high-resolution observations with a limited field-of-view can be converted into approximations of disk-integrated spectra using the newly developed Numerical Sun-as-a-Star Integrator (NESSI). Additionally, I will discuss the impact of projectional effects on the study of such events with focus on the detection of coronal mass ejections. Our findings suggest common patterns in the disk-integrated spectra between flares of different strengths and locations that can be used to better interpret stellar flares without resolved context.

Improved atomic models to interpret the solar radiation emitted from the Transition region and chromosphere

We have long-standing issues and discrepancies between predicted and observed emissions. In the solar transition region and chromosphere, some are due to the inherent limitations of the physical models, but some are due to simplified atomic models.

We developed improved modelling of the ion balance, including physical effects which occur all the time and made them available via the CHIANTI v.11. I will briefly describe them and show how they improve the comparisons with observations of the Sun and other stars, with very simple 1D static atmospheric models.  I will then describe current models we are developing to explain some chromospheric lines, and the plans to include other effects such as photo-ionization.