Physics and Chemistry of Planet-Forming Disks in Extreme Radiation Environments

Our knowledge about the formation history of planetary systems is obtained by comparing the demographics of proto-planetary disks with the exoplanetary system population. Most of the disks that we have been able to characterize to date are located in nearby low-mass star forming regions.

However, it is well known that most stars form in denser environments close to massive stars and therefore are subject to strong far-ultra violet (FUV) radiation affecting the dust and gas in the disk, shortening their lifetime.

It is questionable that the well-studied population of planet forming disks is representative of those in which most exoplanets were assembled.

Due to their large distances and high densities, so far, the only irradiating disks which could be studied are the famous proplyds in Orion.

The FUV radiation is produced by just one massive O star, where the proto planetary disks only get strongly irradiated for a small fraction of their lifetime when their orbit brings them close to the O star.

It has, however, been impossible to study the physical and chemical properties of these proto-planetary disks larger massive star-forming regions, where they are irradiated constantly by several OB stars.With the arrival of the James Webb Space Telescope and its exquisite spatial resolution this is changing and we will obtain high quality MIRI spectra of 15 sources subject to different amount of radiation, located in the same star forming region.

This will allow us to study the molecular line emission as a function of FUV field strength. We will study the survival of Polycyclic Aromatic Hydrocarbons in the irradiated disks as well as the dust composition.

We will compare these findings with theoretical disk models, literature studies and MIRI spectra taken by the GTO team on more isolated disks, not subject of a strong FUV field.Follow-up imaging and optical spectroscopy of the disk-bearing stars is on the way to properly characterize the host stars and derive their temperature and mass as well as foreground extinction.

This allows the construction of a unique spectral energy distribution from optical to the mid-infrared.

We will fit the distributions with circumstellar disk models to derive their geometry, evolutionary state and physical properties.This project exploits the unique resolution and sensitivity of JWST/MIRI to explore for the first time the impact of disk evaporation on the disk structure, warm disk chemistry, and dust mineralogy, all of which are important for planet formation models and exoplanet atmosphere composition.