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Astronomy Colloquium (9.29/2021)：Brown dwarf desert or valley: a comprehensive survey of brown dwarfs based on combined RV and astrometry method
Description
Title: Brown dwarf desert or valley: a comprehensive survey of brown dwarfs based on combined RV and astrometry method
Speaker: Fabo Feng（冯发波）
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 evidences for a brown dwarf valley instread of a desert as proposed in previous studies. This valley 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.
Bio: Fabo Feng is a T.D.Lee fellow at the Tsung-Dao Lee Institute, Shanghai Jiao Tong University. He obtained his PhD at the Max Planck Institute for Astronomy, Germany, in 2015. After that, Fabo moved to the Unversity of Hertfordshire, UK, for his postdoc research on exoplanet detection using the radial velocity method. His work in the UK led to the discovery of the smallest exoplanet ever detected using the radial velocity method. In 2018, Fabo started to work at the Carnegie Institution for Science in Washington D.C., USA, and has found more than 40 exoplanets, including 5 in their habitable zones. In 2020, he became a faculty member of TDLI and his research interests include detecting exoplanets using astrometry and PEXO-based high precision astrophysics as well as interdisciplinary science.
Time: 10:00-11:00AM, 29/Sep, Wednesday
Venue: Room 508 (large seminar room), Department of Astronomy
