Project 3.3: Direct imaging & spectra of ultra-cool companions to nearby stars
Most of the directly imaged exoplanets today are very young and warm with spectral type rang- ing from L to T corresponding to effective temperatures larger than 700K. In most cases, the age estimate of the parent stars combined to giant planets evolutionary models bring some constraints on the mass of the discovered planets but large uncertainties remain (Moya et al. MNRAS 405, L81,2010). Indeed, the evolution of massive giant planets (mass, radius luminosity, chemical composition, Teff) is a challenging task that is mainly unconstrained. The recent discovery of the ultra-cool companion (Teff~400K) to the old main sequence G dwarf HD4113A (Cheetham, Ségransan et al. 2018A&A…614A..16C) with SPHERE identify strong discrepancies between several predicted and observed planet parameters (mainly on Teff, Luminosity and mass). This study shows that deriving dynamical masses of such cool objects is critical to better understand the physics of ultra-cool brown dwarfs and giant planets for which almost no constraint exists beside our own Solar System. Following the work on HD4113, this project aims at identifying and studying the physics (chemical composition, evolution, mass determination) of all ultra-cool companions to nearby main sequence stars in the separation range of 10-50AU. Such a challenging feat is now possible thanks to:
- a unique sample of nearby stars with promising low mass companion candidates derived from 20 years of precise radial velocity measurements with CORALIE/HARPS and close to 5 year of astrometric measurements with GAIA.
- state of the art high contrast imaging & Spectroscopic instruments installed on both ground (SPHERE/GPI) and space (JWST) facilities that allow us to detect and characterise faint companions with contrast as high as 300 000 (∆mag=13.5-14) in the near infrared.
HD4113 C detected with SPHERE IRDIS + IFS (Cheetham, Ségransan et al. 2018A&A…614A..16C)
The CARMENES search for exoplanets around M dwarfs. A Neptune-mass planet traversing the habitable zone around HD 180617
Enforcing dust mass conservation in 3D simulations of tightly coupled grains with the PHANTOM SPH code