Very few sub-stellar companions have been found to orbit around main-sequence stars on wide orbits. The long period orbits of these objects are unlikely to be constrained by traditional methods such as transit and radial velocity with their short observational baseline. Thanks to the 24-year time difference between Gaia and Hipparcos, multiple groups are combining the radial velocity, Gaia-Hipparcos proper motion difference and direct imaging methods to characterize known sub-stellar companions. Unlike these groups, we use both proper motion and positional differences between Gaia and Hipparcos to constrain the orbital inclination of sub-stellar companions and thus determine their dynamical masses. By analyzing the data for more than 5000 stars, we find 167 sub-stellar companions with a mass ranging from 5 to 120 Jupiter mass, extending the current sample of similar objects by one order of magnitude. Without correcting for detection bias, we estimate the minimum occurrence rate of the wide-orbit BDs to be 1.3 %, and find a significant BD valley around 40 Jupiter mass. There are also evidence for a valley around the BD-star boundary and weak evidence for a sharp decrease of occurrence rate around planet-BD boundary, suggesting different formation and evolution scenarios for planets, BDs, and stars. This sample will be important targets for future direct imaging surveys conducted by JWST, CSST and ground-based facilities.
BIO
Fabo is a T.D.Lee fellow of 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, he moved to the Unversity of Hertfordshire, UK, for his postdoc research on exoplanet detection. 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 exoplanet detection, time series analysis, relativity test, interstellar object, Oort Cloud, Galactic dynamics, and interdisciplinary topics.
Host: Sharon Xuesong Wang
