<i>Spitzer</i> thermal phase curve of WASP-121 b

Aims. We analyse unpublished Spitzer observations of the thermal phase-curve WASP-121 b, a benchmark ultra-hot Jupiter. Methods. adopted wavelet pixel-independent component analysis technique to remove challenging instrumental systematic effects in these datasets and we fit them simultaneously with parametric light-curve models. also performed retrievals better understand horizontal vertical structure planetary atmosphere. Results. measured brightness temperatures ~2700 K (dayside) ~700–1100 (nightside), along modest peak offsets 5.9° ± 1.6 (3.6 µm) 5.0° −3.1 +3.4 (4.5 after mid-eclipse. These results suggest inefficient heat redistribution atmosphere b. The inferred atmospheric Bond albedo circulation efficiency align well observed trends for hot giant exoplanets. Interestingly, correspond westward spot, which has rarely been observed. report consistent transit depths at 3.6 4.5 µm, updated geometric orbital parameters. Finally, compared our previous measurements, including recent JWST observations. Conclusions. extracted new information on properties dynamics an exoplanet from especially problematic dataset. This study probes reliability parameters obtained when state-of-the-art pipelines are effects. It demonstrates that provide useful baseline comparison observations, shows increase precision achieved newer telescope.