Atmospheric composition of WASP-85Ab with ESPRESSO/VLT observations

Transit spectroscopy is the most frequently used technique to reveal the atmospheric properties of exoplanets. At high resolution, it has the added advantage of resolving the small Doppler shift of spectral lines and, thus, the trace signal of the exoplanet atmosphere can be extracted separately. We obtained the transmission spectra of the extrasolar planet WASP-85Ab, a hot Jupiter in a 2.655-day orbit around a G5, V = 11.2 mag host star, observed by the high-resolution spectrograph ESPRESSO at the Very Large Telescope array for three transits. We present an analysis of the Rossiter-McLaughlin (RM) effect on WASP-85A and determine a spin-orbit angle lambda = -16.155 degrees(+2.916)(-2.879), suggesting that the planet is in a nearly aligned orbit. Combining the transmission spectra of three nights, we tentatively detected Ha and Ca II absorption with greater than or similar to 3 sigma via direct visual inspection of the transmission spectra with the center-to-limb variation and the Rossiter-McLaughlin effects removed; these absorptions still remain visible after excluding the cores of these strong lines with a 0.1A mask. These spectral signals appear likely to have originated from the planetary atmosphere, but we cannot fully exclude a stellar origin. Via the cross-correlation analysis of a set of atoms and molecules, Li I is marginally detected at the similar to 4s level, suggesting that Li might be present in the atmosphere of WASP-85Ab.

Automated summary

Transit spectroscopy is a commonly used technique to study the atmosphere of exoplanets. In this study, the transmission spectra of WASP-85Ab were obtained and Ha, Ca II, and Li I absorptions were tentatively detected.