WASP-128b: An inflated brown dwarf companion to a Sun-like primary

Brown dwarfs share remarkable similarities with giant planets such as size and atmospheric composition, but are easier to study than exoplanets.  Transiting brown dwarfs provide empirical measurements of their sizes, which combined with their masses allow us to constrain the mass-radius relation of low-mass objects. Of particular interest are inflated gaseous objects, where we know little of the mechanisms behind their sustained inflation. In this context, we report the discovery of WASP-128b, a ~40 Mjup likely inflated brown dwarf companion to a Sun-like primary on a ~2.2 day orbit. After identifying a periodic transit signal with WASP, we obtained radial velocity observations from CORALIE and HARPS and several light curves with the Euler and TRAPPIST telescopes. In this presentation, we present our analysis of these data using a new flexible binary and planet fitting software, and discuss our results in the context of other low-mass objects.

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