Characterizing ultracool dwarfs on the search for exoplanets : the SPECULOOS project & the Trappist-1 system

The SPECULOOS project will be Searching for habitable Planets EClipsing ULtra-cOOl Stars, and will soon start looking at ultra-cool stars in our galaxy with four 1m robotic telescopes located at the ESO Paranal Observatory (Chile). The main goal is to find transiting Earth-sized planets in the habitable zone and provide potential targets for the Extremely Large Telescopes and the James Webb Space Telescope which can do atmosphere studies and search for biomarkers. A prototype program for the SPECULOOS project was carried out on the TRAPPIST telescope, by targeting the brightest ultra-cool dwarfs of the Southern hemisphere to search for transiting planets. This TRAPPIST program has led to the recent discovery of seven terrestrial planets orbiting a M8 dwarf at approximately 11 parsecs from Earth, known as the TRAPPIST-1 system (Gillon et al. 2017). We present this discovery and its newest results from the Kepler-2 mission where a long-cadence analysis confirmed the period of Trappist-1h (18.77 days), thus all seven planets being in orbital-resonance (Luger et al. 2017). In Luger et al. 2017, we find that the star shows flares consistent with a low-activity, middle-aged, late M dwarf. What are the implications of such a host-star to the habitability of the system? Studying and characterising the host-star is extremely important in the field of exoplanet research as it sets the constraints for the potential to sparkle life. At the University of Liège, we have recently adapted our in-house stellar evolutionary code CLES (Scuflaire et al. 2008) to precisely account for these kind of stars. With such improvement, we are able to set new constrains on the mass of Trappist-1 that could account for a middle-aged, ultra-cool dwarf star.