Protoplanetary disks are natural byproducts of the star formation process, when molecular clouds contract due to gravity. After the central stars have formed, the leftover gas and dust will accumulate in such disks and continue to rotate around the new-born stars on nearly circular orbits for a few million years. Planets can then form in these disks, and the outcome will depend on the physico-chemical state in the disks.
The research group "Planet-forming disks and astrochemistry" develops models to understand and simulate the chemical and heating/cooling processes in such disks, which are closely coupled to the continuum and line radiative transfer. Beside the usual 2-body and 3-body reactions, ice formation, surface chemistry, and ionisation are included, as well as dissociation processes triggered by FUV, EUV, X-rays and cosmic rays. The resulting chemical structures depend on the mass and shape of the disk, the size and distribution of dust grains as well as on the irradiation from the central star and the interstellar environment. Based on the computed chemical and temperature structures, a number of continuum and line observations can be predicted, for example spectral energy distributions (SEDs), line fluxes, line velocity profiles, channel maps, and visibilities, as well as line-crowded IR-spectra of varying resolution, see figure below.
The predictions can then be compared to the real observations to determine some of the physical and chemical properties in these disks. Such results have been published for Spitzer/IRS data (SED, mid-IR line fluxes), VLT/CRIRES (CO ro-vib), VLT/PIONEER (H-band visibilities), Herschel (far-IR continuum & lines), ALMA (millimetre continuum & lines) as well as the data from radio telescopes.
The ambitious aim is to combine such multi-wavelength and multi-kind observations, and to find models that can reproduce all of them based on a single disk model; from the hot inner rim (~1500 K) to the cold outer regions (~10 K), from the thin, hot and ionised upper layers down to the dense, cold and neutral midplane. Another research goal is to link the physico-chemical state in the discs, as predicted from the models, to the properties of exoplanets that form in them.
In the FP7 SPACE project DIANA, the disk models were introduced, a large amount of multi-wavelength observational data, for about 30 objects, was collected and analysed and each data set was fitted with one disk model. Some of these fitted disk structures and properties can be studied here.
In the EU Marie-Curie project CHAMELEON, exoplanet experts from six European universities collaborate to develop common strategies for modelling and data interpretation, and to bridge the gap between protoplanetary disks and the properties of exoplanets that form in them.