TRANSMISSION SPECTROSCOPY OF THE HOT JUPITER WASP-12b FROM 0.7 TO 5 μm

Abstract

Since the first report of a potentially non-solar carbon-to-oxygen ratio\n(C/O) in its dayside atmosphere, the highly irradiated exoplanet WASP-12b has\nbeen under intense scrutiny and the subject of many follow-up observations.\nAdditionally, the recent discovery of stellar binary companions ~1" from\nWASP-12 has obfuscated interpretation of the observational data. Here we\npresent new ground-based multi-object transmission-spectroscopy observations of\nWASP-12b that we acquired over two consecutive nights in the red optical with\nGemini-N/GMOS. After correcting for the influence of WASP-12's stellar\ncompanions, we find that these data rule out a cloud-free, H2 atmosphere with\nno additional opacity sources. We detect features in the transmission spectrum\nthat may be attributed to metal oxides (such as TiO and VO) for an O-rich\natmosphere or to metal hydrides (such as TiH) for a C-rich atmosphere. We also\nreanalyzed NIR transit-spectroscopy observations of WASP-12b from HST/WFC3 and\nbroadband transit photometry from Warm Spitzer. We attribute the broad spectral\nfeatures in the WFC3 data to either H2O or CH4 and HCN for an O-rich or C-rich\natmosphere, respectively. The Spitzer data suggest shallower transit depths\nthan the models predict at infrared wavelengths, albeit at low statistical\nsignificance. A multi-instrument, broad-wavelength analysis of WASP-12b\nsuggests that the transmission spectrum is well approximated by a simple\nRayleigh scattering model with a planet terminator temperature of 1870 +/- 130\nK. We conclude that additional high-precision data and isolated spectroscopic\nmeasurements of the companion stars are required to place definitive\nconstraints on the composition of WASP-12b's atmosphere.\n