FOR 2634:  Planet Formation Witnesses and Probes: Transition Discs

• Subject Area: Physics
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 325594231

Recent surveys have shown an overwhelming diversity of extrasolar planetary systems, prompting the question of how did they form, and whether some may end up looking like our own and being able to sustain life. Planets are born out of the dust and gas left over whenever a new star forms: the protoplanetary disk. The initial conditions for planet formation are thus determined by the protoplanetary disks, which evolve and disperse as they give birth to planets. Interestingly, the timescales of disk dispersal are comparable to those of planet formation. Disks on the verge of dispersal, so-called “Transition Disks” (TDs), are thus particularly important witnesses of the planet formation process, and they can be used as probes of the different mechanisms at play at this crucial time of disk evolution. TDs, which are usually identified as disks showing evidence of an evacuated inner dust hole, are in reality a diverse class of objects. Some TDs have small dust holes and are weakly accreting. Others have much larger inner dust cavities and vigorous accretion. Different physical processes may be at play for the formation of different TD types (e.g. photoevaporation, MHD processes, dust evolution, planet-disk interactions), each being a piece of the complex planet formation puzzle. Due to the lack of spatial resolution of telescope facilities, until recently, observations of protoplanetary disks provided very few constraints on our understanding of disk evolution and planet formation. The situation has now improved thanks to facilities like ALMA and VLTSPHERE. At near infrared and millimetre wavelengths we now start to obtain extraordinarily detailed images of these disks. They turn out to feature complex structures, including lopsided blobs, rings, spirals etc., that challenge our theoretical understanding of these disks. Some of these structures may be caused by newly formed giant planets that gravitationally perturb the disk, but new alternative explanations are also emerging. In our proposed Research Unit we aim at studying various aspects of TDs, to better understand their different formation mechanisms. Only understanding the disk evolution and the planet-disk interactions allow the large body of existing and planned observations to be exploited to answer more complex questions like the formation of planetary systems capable to host life. This requires a focussed effort from several communities to devise a multi-pronged strategy to tackle the problem. Specifically, multiwavelength observations of disks at different stages of evolution together with exoplanet and disk statistics should be used to constrain a concerted theoretical modelling effort including the hydrodynamics of the dust and gas component of disks, with and without planets, joint to chemical and radiative transfer calculations, particularly of the surface layers and winds of disks in (or just before) the transition phase. This is the motivation for the proposed Research Unit.

• DFG Programme: Research Units
• International Connection: Chile, China, France, Italy, Netherlands, United Kingdom, USA

Projects

• Coordination Funds (Applicant Ercolano, Ph.D., Barbara )
• Disk population study: observational constraints (Applicant Miotello, Ph.D., Anna )
• Disk Population Synthesis (Applicant Birnstiel, Tilman )
• From Transition Disks to Debris Disks (Applicants Birnstiel, Tilman ;  Dullemond, Cornelis Petrus )
• Gone with the wind: dust entrainment in photoevaporative winds (Applicant Ercolano, Ph.D., Barbara )
• New constraints on disk-dissipation processes from the relation between accretion and X-ray activity (Applicant Preibisch, Thomas )
• Origin of complex non-axisymmetric structures in Type 2 Transition Disks (Applicant Dullemond, Cornelis Petrus )
• Probing the inner planet-forming zones of disks with mid-infrared spectroscopy (Applicant van Dishoeck, Ewine F. )
• Solids and gas evolution in disks: observational constraints (Applicant Testi, Leonardo )
• The radiation-hydrodynamics of photoevaporative winds with chemistry (Applicant Ercolano, Ph.D., Barbara )
• Thermally-assisted magentocentrifugal outflows – theoretical predictions and observational signatures (Applicants Ercolano, Ph.D., Barbara ;  Gressel, Oliver )
• Thermochemistry of disc winds and atmospheres (Applicant Ercolano, Ph.D., Barbara )
• Transition disks and planetary systems (Applicant Dullemond, Cornelis Petrus )

• Spokesperson: Professorin Dr. Barbara Ercolano, Ph.D.