Speaker
Description
State-of-the-art spectrographs on large ground-based telescopes have allowed significant discoveries in the structure, composition and dynamic processes of exoplanetary atmospheres through high-resolution transit spectroscopy. However, observations from ground-based facilities face two major challenges : The day-night cycle limits the length of observations, and incoming signals are distorted by Earth's atmosphere. The latter can be solved by adaptive optics and precise telluric correction, but the former is an issue for transit spectroscopy. This restricts the observable planets to ones with transit duration smaller than five hours.
Extremely inflated exoplanet KELT-11b is affected by this issue, as it transits its host star for more than seven hours. To bypass this limitation, we observed this system for series of three consecutive days: Before, during and after the transit, in order to collect a large number of in-transit and out-of-transit baseline spectra. This allowed the computation of a strong signal-to-noise high-resolution combined transmission spectrum. The individual spectra were corrected for telluric absorption using ESO atmospheric transmission code Molecfit.
This resulting transmission spectrum shows conclusive evidence of excess atomic sodium absorption through the 5'900 Å doublet of 0.29±0.05 % and 0.50±0.06 % in the Na D1 and D2 lines respectively. We model for wind patterns and find day-to-night side winds with surprisingly no vertical winds, considering KELT-11b's extreme scale height of 2'763 km. We also highlight the robustness of our three-day observation method which allows the study of exoplanets with long transits that haven't been studied with high-resolution ground-based spectrographs.
Other recent results from TESS, HST and CHEOPS combined with KELT-11b's hot atmosphere, bright host star, long transit, sub-Saturn mass and great bloatedness make it a unique and ideal candidate for atmospheric characterization with the next generation of telescopes, especially from space.
