Name/Affiliation: Taisiya Kopytova (MPIA)
Chemical abundance of brown dwarfs as a key to formation scenario
We present our spectroscopic study of directly imaged exoplanets and brown dwarf companions using VLT/SINFONI, and their hosts using FEROS at La Silla. We derive [Fe/H] and the C/O ratio for the companions and hosts, which helps us to distinguish between the core accretion and the disk instability scenarios for formation of the companions. Previous studies showed that metal-rich stars have more massive planets. This could be an outcome of the core accretion formation theory. The larger the metallicity of the disk, the faster the core is formed and more gas can be accreted onto it. Lower-mass planets do not accrete large amounts of gas over the timescale of core formation, therefore, they are less sensitive to the disk metallicity. Due to different condensation temperatures of carbon and oxygen, the C/O ratio is different at different parts of a protoplanetary disk and depends on the disk temperature profile. Therefore, the C/O ratio of a companion formed by core accretion can vary and will reflect that of the part of the disk where it formed. Conversely, companions formed by disk gravitational instability are expected to have C/O ratios consistent with their host stars. We present the very first study using this approach and put constraints on the application of this method for testing formation scenarios of exoplanets and brown dwarfs.