The LRG-BEASTS transmission spectroscopy survey: WASP-39b
James Kirk
Smithsonian Astrophysical Observatory



I will present results on the latest exoplanet to be studied by the Low Resolution Ground-Based Exoplanet Atmosphere Survey using Transmission Spectroscopy (LRG-BEASTS, "large beasts"), the hot Saturn-mass exoplanet WASP-39b. This is one of the very best targets for transmission spectroscopy, with a transit depth per atmospheric scale height of 450 ppm. As a result, this exoplanet has been studied by several groups. However, these studies have reported atmospheric metallicities for this exoplanet which differ by orders of magnitude and in turn lead to different conclusions about the exoplanet's formation. This motivated us to perform a new retrieval analysis on all literature data sets, combined with our new optical transmission spectrum, to try and resolve the discrepancies in the literature, which are a concern given how amenable this exoplanet is to characterisation. WASP-39b has one of the most cloud- and haze-free atmospheres of hot, giant exoplanets, which show a remarkable diversity across the population, from clear to cloudy atmospheres. LRG-BEASTS will sample this diversity with observations of 17 exoplanets covering a broad range of temperatures (825 to 2500K) and masses (0.2 to 1.5 Jupiter masses), while providing optical data useful for constraining abundances derived from infrared data. LRG-BEASTS is pioneering the use of 4-metre class telescopes for low resolution transmission spectroscopy. To date, LRG-BEASTS has published results for 3 exoplanets (HAT-P-18b, WASP-52b and WASP-80b) and has demonstrated that such telescopes can provide precision comparable to VLT and HST.