C/O ratio as a Dimension for Characterizing Exoplanetary AtmospheresProposes a 2-dimensional classification scheme: oxygen-rich (O) vs carbon-rich (C), low irradiation (1) vs high irradiation (2). The irradiation boundary for O-type planets is at the critical flux for thermal inversion, estimated to be in the range 1–5×10
9 erg/s/cm
2 (gotta love astronomers and their CGS units). O1 and O2 roughly correspond to the pL and pM classes that have been previously mentioned. For C-type planets the division is set at T=1200 K, motivated by the depletion in abundance of H
2O and enrichment of CH
4 with respect to O-type planets.
Six systems are considered:
XO-1b: C2
CoRoT-2b: tentative C2
WASP-14b: either O1 or C2, the oxygen-rich classification is a marginally better fit to the data
WASP-19b: tentative C2
WASP-33b: either O2 or C2, the carbon-rich classification is a marginally better fit to the data
WASP-12b: C2