Find the Boundary of Brown Dwarf Desert: a Comprehensive Survey of Brown Dwarfs Based on Combined RV and Astrometry Method
Title: Find the Boundary of Brown Dwarf Desert: a Comprehensive Survey of Brown Dwarfs Based on Combined RV and Astrometry Method
Speaker: Professor Fabo Feng (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)
Time: 10:30am, November 8, 2021
Location: 3-302, PMO Xianlin Campus
Abstract: Very few brown dwarfs have been found to move around main-sequence stars on Jupiter-like or closer orbits. Previous surveys failed to explore this population due to limitation of the transit and radial velocity methods. Thanks to the unprecedented precision of Gaia astrometry data, multiple groups are trying to combine the radial velocity, astrometry and direct imaging methods to find circum-stellar brown dwarfs. Unlike previous studies, we have used both the proper motion and positional difference between Hipparcos and Gaia to find astrometric signals of companions with much lower mass. This allows us to find nearly 200 companions with a mass between 5 to 120 Jupiter mass, doubling the known sample of cold jupiters and brown dwarfs. The mass distribution of our sample shows strong evidence for a brown dwarf desert boundary at around 5 au. This boundary is probably shaped by the competition between the planet-formation and star-formation channels of brown dwarfs. We also find dozens of multi-companion systems and explore the possible mechanisms for orbital misalignment. This sample will be important targets for future direct imaging surveys conducted by JWST, CSST and ground-based facilities.