Direct imaging and characterization of low mass companions to young early-type stars

Séminaire IPAG de Mickael Bonnefoy (MPIA), jeudi 21 février 2013 à 11h00, IPAG seminar room

Abstract : High contrast imaging is the only viable technique nowadays to probe the population of wide (> 5 AU) giant planets and brown dwarfs around young stars (< 150 Myr) of the solar neighborhood (d < 100 pc). Recent breakthrough detections of gaseous companions at relatively short separations (8-78 AU) around young early-type stars (HR 8799, β Pictoris) with this technique have motivated new surveys to look for gas giant planets around similar or even more massive (B-type) stars. These discoveries have also triggered numerous theoretical studies to understand the formation of these systems. These theoretical efforts relies on our capability to achieve a good characterization of the companions properties (mass, semi-major axis, effective temperature) from their astrometry, photometry, and spectra.

During this seminar, I will present results from observation campaigns on 8-m class telescopes which aim to detect new companions around massive stars and/or characterize their physical and chemical properties. One program, conducted during the Subaru Strategic Exploration of Exoplanets and Disks Survey (SEEDS) on the HiCIAO high-contrast imager, recently led to the discovery of a companion at the planet/brown-dwarf boundary at a projected separation of 55 +- 2 AU around the late B-type star κ Andromedae. The host star’s estimated mass of 2.4–2.5 Msun places it among the most massive stars ever known to harbor an extrasolar planet or low-mass brown dwarf. I will show new images of this system collected on Keck/NIRC2 and on the LMIRCam infrared camera at LBT (fed by the most advanced adaptive optics system actually on-sky) which helped to refine the properties (mass, effective temperature) of the companion. I will also present results from a program on NaCo which enabled for the first time to build the near-infrared spectral distribution of the giant planet (1.2-5.8 µm) β Pictoris b and to refine estimates on its mass, effective temperature , and orbital parameters. I will show what constraints κ Andromedae b and β Pictoris b properties bring on current giant planet formation scenarios.