High resolution atmospheric retrievals of WASP-76b transmission spectroscopy with ESPRESSO: Monitoring limb asymmetries across multiple transits

Abstract

Direct atmospheric retrievals of exoplanets at high resolution have recently allowed for a more detailed characterisation of their chemistry and dynamics from the ground. By monitoring the longitudinal distribution of species across multiple transits, as well as the varying vertical temperature structure and dynamics between the limbs of WASP-76b, we aim to enhance our understanding of the 3D nature and chemical and dynamical evolution of such objects over timescales of months to years. We present retrievals of three VLT/ESPRESSO observations of the ultra-hot Jupiter WASP-76b, including one not yet reported in the literature, from which we constrain the atmospheric abundances, vertical temperature structure, and atmospheric dynamics for the leading and trailing limbs of the atmosphere separately, via novel rotational broadening kernels. We confirm the presence of VO recently reported in the atmosphere of WASP-76b. We find a uniform longitudinal distribution of Fe and Mg across the limbs of the atmosphere for each of the transits, which is consistent with previous works as well as with stellar values. We constrain substellar Na/Fe and Cr/Fe ratios across each of the transits, which is consistent with previous studies of WASP-76b. Where constrained, V/Fe and VO/Fe ratios were also found to be broadly consistent between the limbs of the atmosphere for each of the transits, as well as with previous studies. However, for two of the transits, both V and VO were unconstrained in the leading limb, suggesting a possible depletion due to recombination and condensation. The consistency of our constraints across multiple high resolution observations, as well as with previous studies that used varying modelling and retrieval frameworks and/or instruments, affirms the efficacy of high resolution ground-based retrievals of exoplanetary atmospheres.