Research - Demographics Statistical properties of Giant Planets

 Context and goals

With the manna of exoplanet discoveries since the 51 Peg b announcement, the diversity of systems found (Hot Jupiters, irradiated and evaporating planets, misaligned planets with stellar spin, circumstellar and circunbinary planets in binaries, telluric planets in habitable zone, discovery of Mars-size planet...), the theories of planetary formation have drastically evolved to digest these observing constraints. However, we are still missing the fullpicture and some key fundamental questions still lack answers like: the physical processes at play to pass thekm-size barrier to form planetary cores, the physics of accretion to form planetary atmospheres, the formation mechanisms to explain the existence of giant planets at wide orbits, the physical properties of young Jupiters,the impact of planet-planet and planet-disk interaction in the final planetary system architecture, the influence of the stellar mass and stellar environment in the planetary formation processes. Neither core accretion plus gas capture (CA), even with alternattive processes like pebble nor disk fragmentation driven by gravitational instabilities (GI) can globally explain all current observable from planet hunting techniques. Alternative mechanisms are then proposed, such as pebblesaccretion to enable CA to operate at wide orbits, inward/outward migration or planet-planet or simply the possibility to have several mechanisms forming giant planets operating in concert. A stellar-like mechanism like gravo-turbulent fragmentation could be also an alternative solution to form massive planetary mass companions at wider separations (≥5−10 au) in the earliest phase of the disk’s lifetime. In this context, one final key element addressed by direct imaging surveys concerns the occurrence of giant planets beyond 5 au to actually test these theories. Past and current surveys, independently of the technique used, have shown that the occurrence rate of giant planets, more massive than Jupiters, in nearby systems is a few percents at most (Bowler 2016, Fernandes et al. 2019). Demographics studies of this population therefore require the observation of large samples and significant amounts of observing time. Discoveries together with the non-detection can be used to actually derive the survey completeness and the frequency of the giant planet population that can be directly compared to the predictions of planet population synthesis models.

SHINE, SpHere INfrared survey for Exoplanets

Following pioneer studies with NaCo that enable to provide first constraints on the demographics of giant planets beyond 30 to 40\,au (Chauvin et al. 2010, 2015; Rameau, Chauvin et al. 2013), the SpHere INfrared survey for Exoplanets (SHINE) of 600 stars from the SPHERE Guaranteed Time Observations (GTO), that I lead, is starting to provide unique statistical constraints on the demographics of giant planets beyond 10 au (see the mean survey detection probability compared to that from the first generation of planet imagers). Given the unprecedented detection performances achieved by SPHERE, the early statistical results considering a sample of 150 stars demonstrate that giant planets are relatively rare beyond 10\,au, finding a a rather low frequency of planetary systems hosting at least one giant planet between 10 to 1000 au with an estimated valueof 5.7+3.9−2.8% for massive (≥ 0.5MJup) giant planets around solar-type stars aged of 50-500 Myr. The size and stellar properties of the SHINE sample will still enable constraints on the variation of exoplanet occurrence rate with stellar mass and age. The final survey completeness will also be directly compared to the current predictions from planetaryformation models to test the efficiency of each physical process (core accretion, gravitational instability, migration, dynamical scattering, ejection). The fundamental questions that will be addressed by the SHINE final survey are:

• What is the occurrence of giant planets and brown dwarf companion around young, nearby stars?

• How does this occurrence vary with the mass of the stellar host?

• Are we able to identify two populations of objects (brown dwarfs and exoplanets) with different mass, separation, eccentricity distributions and occurrence tracing different history of formation?

Key publications

Early publications related to the demographics of Young Jupiters:

• Chauvin, G., Lagrange, A. -M., Bonavita, M., Zuckerman, B. et al. 2010, Astronomy and Astrophysics Deep imaging survey of young, nearby austral stars . VLT/NACO near-infrared Lyot-coronographic observations

• Chauvin, G., Vigan, A., Bonnefoy, M., Desidera, S., Bonavita et al. 2015, Astronomy and Astrophysics The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits. II. Survey description, results, and performances

• Rameau, J., Chauvin, G., Lagrange, A. -M., Klahr, H., Bonnefoy, M., Mordasini, C., Bonavita, M., Desidera, S., Dumas, C., & Girard, J. H. 2013, Astronomy and Astrophysics A survey of young, nearby, and dusty stars conducted to understand the formation of wide-orbit giant planets. VLT/NaCo adaptive optics thermal and angular differential imaging

Early results from the SpHere INfrared survey for Exoplanets:

• Desidera, S., Chauvin, G., Bonavita, M. et al. 2021, arXiv e-prints The SPHERE infrared survey for exoplanets (SHINE)- I Sample definition and target characterization

• Langlois, M., Gratton, R., Lagrange, A. -M., Delorme, P., Boccaletti, A., Bonnefoy, M. et al. 2021, arXiv e-prints The SPHERE infrared survey for exoplanets (SHINE) -- II. Observations, Data reduction and analysis Detection performances and early-results

• Vigan, A., Fontanive, C., Meyer, M., Biller, B., Bonavita, M., Feldt, M., Desidera, S., Marleau, G. -D., Emsenhuber, A., Galicher, R., Rice, K., Forgan, D., Mordasini, C., Gratton, R., Le Coroller, H., Maire, A. -L., Cantalloube, F., Chauvin, G. et al. 2020, arXiv e-prints The SPHERE infrared survey for exoplanets (SHINE). III. The demographics of young giant exoplanets below 300 au with SPHERE

Collaborators

SHINE team management: Gaël Chauvin (PI), Silvano Desidera, Janis Hagelberg, Anne-Marie Lagrange, Raffaele Gratton, Maud, Langlois, Michkael Bonnefoy, Arthur Vigan, Michael Meyer, Markus Feldt

SHINE team at IPAG: Philippe Delorme, Julien Milli, Mickael Bonnefoy, Simon Petrus, Célia Desgrange, François Ménard, Jean-Charles Augereau, Myriam Benisty

Population synthesis: Christoph Mordasini, Gabriel Marleau, Martin Schleker, Hubert Klahr, Duncan Forgan, Ken Rice