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

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 Hα, Hβ, and Hγ 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 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.