Combining optical ground-based low- and high-resolution transmission spectroscopy data: tight constraints on sodium abundance of WASP-94Ab

In this talk I will present evidence for pressure-broadened sodium absorption and a steep scattering slope, using both high- and low-resolution optical transmission spectra of the hot Jupiter WASP-94Ab. Broad sodium is an indicator of a cloud-free atmosphere, suggesting the highly-inflated WASP-94Ab is an excellent target for molecular abundance determination using infrared spectroscopy.

On its own, our low-resolution transmission spectrum in the wavelength range of 3800–7140 Å has revealed a clear atmosphere with a 4.9σ sodium absorption and a scattering slope through the LRG-BEASTS survey. It was measured with the EFOSC2 spectrograph on the ESO New Technology Telescope — the first time this instrument has been used for transmission spectroscopy. The high resolution spectrum is from HARPS (taken as part of the HEARTS survey), probing the Doppler shifts of the sodium line doublet.

In this talk I will present a detailed study of the atmosphere of this exoplanet, a highly-inflated hot Jupiter with a radius of 1.7 Jupter radii and a mass of 0.5 Jupiter masses and an estimated equilibrium temperature of 1500 K. I will discuss the analysis of both low- and high-resolution observations and its independent results, as well as the additional constraints that are achieved from a combined analysis. The latter of which provides an increase in the robustness and the precision on the measured value. In future, more combined observations will provide high precision abundances for such species, particularly when signals may be weak or when high altitude clouds and hazes are present.