Storms or systematics? The changing secondary eclipse depth of WASP-12b

Hooton, M. J., De Mooij, E. J. W., Watson, C. A., Gibson, N. P., Galindo Guil, F. J., Clavero, R., Merritt, S. R. 2019. Storms or systematics? The changing secondary eclipse depth of WASP-12b. Monthly Notices of teh Royal Astronomical Society 486, 2, 2397-2406 DOI: 10.1093/mnras/stz966

WASP-12b is one of the most well-studied transiting exoplanets, as its highly inflated radius and its 1.1 d orbit around a G0-type star make it an excellent target for atmospheric categorization through observation during its secondary eclipse. We present two new secondary eclipse observations of WASP-12b, acquired an year apart with the Wide Field Camera on the Isaac Newton Telescope (INT) and the IO:O instrument on the Liverpool Telescope (LT). These observations were conducted in the i’ band, a window expected to be dominated by titanium oxide features if present in appreciable quantities in the upper atmosphere. We measured eclipse depths that disagree with each other by similar to 3 sigma (0.97 +/- 0.14 mmag on the INT and 0.44 +/- 0.21 mmag on the LT), a result that is mirrored in previous z’ band secondary eclipse measurements for WASP-12b. We explore explanations for these disagreements, including systematic errors and variable thermal emission in the dayside atmosphere of WASP-12b caused by temperature changes of a few hundred Kelvin: a possibility we cannot rule out from our analysis. Full-phase curves observed with TESS and CHEOPS have the potential to detect similar atmospheric variability for WASP-12b and other optimal targets, and a strategic, multitelescope approach to future ground-based secondary eclipse observations is required to discriminate between explanations involving storms and systematics.

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