Mining the Ultrahot Skies of HAT-P-70b: Detection of a Profusion of Neutral and Ionized Species

Abstract

With an equilibrium temperature above 2500 K, the recently discovered HAT-P-70b belongs to a new class of exoplanets known as ultrahot Jupiters: extremely irradiated gas giants with day-side temperatures that resemble those found in stars. These ultrahot Jupiters are among the most amenable targets for follow-up atmospheric characterization through transmission spectroscopy. Here, we present the first analysis of the transmission spectrum of HAT-P-70b using high-resolution data from the HARPS-N spectrograph of a single-transit event. We use a cross-correlation analysis and transmission spectroscopy to look for atomic and molecular species in the planetary atmosphere. We detect absorption by Ca ii, Cr i, Cr ii, Fe i, Fe ii, H i, Mg i, Na i, and V i, and we find tentative evidence of Ca i and Ti ii. Overall, these signals appear blueshifted by a few km s ⁻¹, suggestive of winds flowing at high velocity from the day side to the night side. We individually resolve the Ca ii H and K lines, the Na i doublet, and the H α, H β, and H γ Balmer lines. The cores of the Ca ii and H i lines form well above the continuum, indicating the existence of an extended envelope. We refine the obliquity of this highly misaligned planet to ${107.9}_{-1.7}^{+2.0}$ degrees by examining the Doppler shadow that the planet casts on its A-type host star. These results place HAT-P-70b as one of the exoplanets with the highest number of species detected in its atmosphere.