Using Longitudinally Resolved Spectra on Exoplanet Phase Curves

Jared Splinter ( Université McGill )

Planet atmospheres are intrinsically 3D in nature with thermal phase variations of short period planets show day-to-night temperature contrasts range from hundreds to thousands of degrees. However, spectra of exoplanets are typically fit with use of disk integrated 1D spectral retrieval codes, which assumes the planet’s atmosphere is spherically symmetric. For short-period, tidally locked planets this assumption can be misleading as these planets experience a permanent day-side and night-side. Multi-dimensional spectral retrieval schemes has more recently been introduced for interpreting spectra of short-period exoplanets but these codes come with increased model complexity and computational cost compared to standard 1D codes. However, there is another alternative, phase-dependent spectral observations can be fit with a Fourier series that can be analytically converted to longitudinal maps to produce longitudinally resolved spectra. Longitudinally resolved spectra can be fit using already tested 1D spectral retrieval codes. My work aims to compare these different spectral retrieval methods for exoplanet phase curve observations. I will discuss how I will use these methods on synthetic spectra created from a Global Circulation Model which can be used for comparison. I will then use these techniques on real data of the exoplanet WASP-121b obtained with JWST. Lastly, I will discuss how the spectral retrieval methods can be used in recommended for future ARIEL observations and help find optimal ways of characterizing exoplanet atmospheres.