Falling Evaporating Bodies in young intermediate mass stars: linked with disc structure?

Exoplanets are often found around Main Sequence stars, but around pre-Main Sequence stars (PMS) it is much harder to find them, and only one confirmed case exists so far. Therefore, it is common to look for indirect signatures of planets in the discs around PMS stars. In this talk, I will discuss detections of variable absorption features of metals in the UV spectra of intermediate-mass PMS stars (the so-called Herbig stars), attributed to (in)falling evaporative bodies (FEBs). These features appear to only be present in flat discs (Meeus group II) , and not in the more flared, gapped discs (Meeus group I) that often are thought to host giant planets, causing large gaps. The absence of signatures of FEBs in the UV spectra could be due to a filtration process at the edge of the gap, halting dust and larger bodies that contain material  with high evaporation temperatures (Si, Fe, Mg,..), while the material with low evaporation temperatures (C,N,O) can flow freely as gas towards the star, where it will be accreted. Such a selective accretion process can cause an underabundance of metals in the photosphere of non-convective stars, what can be verified through spectroscopic metallicity studies, and has indeed already been found in several group I discs around Herbig stars (e.g. Kama et al. 2015, A&A 582, L10; Guzman et al. 2023, A&A  671, 140).