The Exotic Atmosphere of an Extreme World: Detection of Ionized Calcium in WASP-76b

Recent observations have revealed a number of atomic species in the atmosphere of WASP-76b, consistent with its ultra-hot temperatures. Here we report new results on this extreme world from transit spectroscopy with the GRACES instrument at the Gemini North Observatory, as part of the Large and Long Program “Exploring the Diversity of Exoplanet Atmospheres at High Spectral Resolution” (PI: Jake Turner). With a broad spectral range of 400 - 1050 nm, our observations can probe previously-detected species while also accessing features beyond the wavelength coverage of earlier works.

In this talk, I will present our recovery of absorption features due to Na I, and report for the first time detections of the ionized calcium (Ca II) triplet at ~ 850 nm in the atmosphere of WASP-76b. After comparing the observed line profiles of the Ca II triplet to model LTE and NLTE spectra, I will discuss the possibility that we are probing the exoplanet’s upper atmosphere, and/or detecting evidence of hydrodynamic outflow.