News: This session is dedicated to the memory of Prof. Dr. Wilhelm ("Willy") Kley.

The main goal of this Special Session is to gather around the table all the specialists in the sub-fields that target the different aspects of the life of a circumbinary P-type exoplanet (i.e. formation, dynamics, long-term evolution, observations and detection) for ensuring a comprehensive approach to the science of such a population, and establishing a exhaustive network of expertises to help deepen our understanding on the nature of these objects.

The hefty number of detected exoplanets showed a large diversity of planetary architectures, including a population of planets in binary systems. These planets are classified into two archetypes: the ones orbiting around one of the two binary components, and the ones orbiting on exterior orbits of compact binaries (where the binary separation is less than 20 au), commonly referred to as "P-type" systems. Due to observational biases, the relatively low detection rate (~40) of planets of the latter type prevents the community from understanding their physical properties and (dynamical) evolution.

How does this population differ from the single star systems ? How does the host binary affect their formation and long term evolution ?

A clear answer to these questions is still pending, and since around half of the stellar population in the Milky Way reside in multiple stellar systems, it is important to deepen our knowledge on such systems, for ultimately unveiling the true nature of the Galactic planetary population.

This special session will cover the three stages of the life of Circumbinary P-type exoplanets:

• Planetary formation: theory and observations on the formation of exoplanets in protoplanetary circumbinary discs. This block wants to provide a global overview on the observational constraints we have set up to today on the properties of circumbinary protoplanetary discs. Consequently, it will discuss their link with the state-of-the-art simulations of the dynamics and evolution of circumbinary discs, circumbinary planet formation and circumbinary planet-disc interactions.



• Main Sequence planets: detection and population studies (observational and theoretical) of main sequence circumbinary exoplanets. Circumbinary planets orbiting main sequence binaries have only been unambiguously identified thanks to the transit method so far. Fourteen planets in 12 systems are known. Despite relatively low numbers, the low probability of transit translates into a relatively high occurrence rate, such that gas giants could exist just as frequently in circumbinary configuration, as in single star systems. Recent work is attempting to bring in other methods such as radial-velocities and astrometry. Radial-velocities appear to show a lack of planets more massive than Jupiters, pointing to differences in the formation process of circumbinary versus circumstellar planets. Furthermore, recent theoretical work also showed that the final orbital properties of circumbinary planets contain information about their protoplanetary disc properties, providing a unique means to study planet formation and disc-driven migration. This block wants to strengthen our knowledge on the link between formation and the observed planetary architectures, and shed light on the processes between these two phases.



• Planets beyond the Main Sequence: (i) Observations and long-term evolution of planets after their binary leave the main sequence, (ii) observations of post-Main Sequence protoplanetary discs, and theory of second generation exoplanets (developed in synergy with the "Planetary Formation" block). Contrary to what we see for the single star planetary systems, several P-type exoplanets have been detected orbiting a binary whose higher mass component is now a White Dwarf. These discoveries prove that planets can survive at least one phase of the binary evolution. This block wants to focus on the effects of binary evolution on the architecture, dynamics, possible ejections of planets from their systems, and possible second generation formation. Furthermore, it aims at improving observational and theoretical constraints on the occurrence rate of these objects, to gain deeper knowledge on how circumbinary planets come to their end.

Programme

The Session will be divided in three blocks. Each block will focus on a specific stage of the life of a circumbinary exoplanet and it will open with an invited review on the topic. Scientific Posters are welcome.

The session is scheduled for Friday 1st July 2022.

Provisional program:

9:00 - 9:05 Welcome (Camilla Danielski)

Planetary formation block (Chair: Rebecca Martin)
09:05 - 09:25 Invited talk (Richard Nelson).
09:25 - 11:53 Contributed talks.

Main Sequence planetary systems block (Chair: Matt Standing)
11:54 - 12:14 Invited talk (Veselin Kostov)
11:35 - 12:45 Contributed talks.

CBPs beyond the Main Sequence block (Chair: Jaques Kluska)
17:30 -17:42 Contributed talk. 17:43 - 18:03 Invited talk (Eva Villaver).
18:04 - 18:30 Contributed talks.
18:30 - 19:00 Discussion covering the 3 blocks.


Note: Contributed talks are 10 min +2 min questions long.

Invited speakers

• Richard Nelson (Queen Mary University of London) -- Planetary Formation
• Veselin Kostov (NASA Goddard Space Flight Center and SETI Institute) -- Planets orbiting Main Sequence binaries
• Eva Villaver (Centro de Astrobiologia, CSIC-INTA) -- Planets beyond the Main Sequence

Scientific organisers

Camilla Danielski (IAA-CSIC, Spain)
Jacques Kluska (KU Leuven, Belgium) - Chair
Amaury Triaud (University of Birmingham, UK)
Matt Standing (University of Birmingham, UK) - Chair
Mariangela Bonavita (Open University, UK)
Wilhelm Kley (Tubingen University, Germany)
Rebecca Martin (University of Nevada, Las Vegas, US) - Chair

Contact

For any questions you can contact Camilla Danielski (cdanielski AT iaa.es) or Jacques Kluska (jacques.kluska AT kuleuven.be) or Mariangela Bonavita (mariangela.bonavita AT open.ac.uk)