Chasing Shadows: Shedding Light on the Nightside Emission of an Ultra Hot Jupiter with SPIRou

Anne Boucher ( Université McGill )

We report the first detection of the diurnal cycle made at high-resolution and for the ultra-hot Jupiter KELT-20b, with CFHT/SPIRou. We measure the variation of the temperature structure for the two hemispheres from H2O features, but also (although less clearly) from CO. H2O and CO are detected at more than 3 sigma, on both day and night hemispheres. As expected, the H2O signal is consistent with an inverted temperature profile (warming with altitude) on the dayside and with a non-inverted profile (cooling with altitude) on the nightside. However, the CO signal is consistent with an inverted profile on both hemispheres, which could be an indication that the nightside CO signal originates from the evening (trailing) limb of the terminator. The radial velocity shifts retrieved for both molecules on each hemisphere, suggest a complex 3D picture of KELT-20b: a CO dominated inverted dayside, with H2O dissociation around the offset hotspot region, and a H2O dominated non-inverted nightside, both of which are subject to advection from eastward jets.