The KPF SURFS-UP Survey I: Transmission Spectroscopy of WASP-76 b

TL;DR

The paper introduces the KPF SURFS-UP survey and pipeline, demonstrating high-resolution transmission spectroscopy of ultra-hot Jupiter WASP-76 b, revealing atmospheric composition, asymmetries, and vertical structure insights.

Contribution

It presents a new high-resolution survey and data pipeline for ultra-hot Jupiters, with the first application to WASP-76 b showing detailed atmospheric detections and asymmetry analysis.

Findings

Detected Fe I at SNR of 14.5 in WASP-76 b

Confirmed Fe I absorption asymmetry, no ingress-egress asymmetry in Na I and Ca II

Revealed vertical atmospheric structure differences in WASP-76 b

Abstract

We introduce the KPF SURFS-UP (Spectroscopy of the Upper-atmospheres and ReFractory Species in Ultra-hot Planets) Survey, a high-resolution survey to investigate the atmospheric composition and dynamics of a sample of ultra-hot Jupiters with the Keck Planet Finder (KPF). Due to the unique design of KPF, we developed a publicly available pipeline for KPF that performs blaze removal, continuum normalization, order stitching, science spectra combination, telluric correction, and atmospheric detection via cross-correlation. As a first demonstration, we applied this pipeline to a transit of WASP-76 b and achieved some of the highest signal-to-noise detections of refractory species in WASP-76 b to date (e.g., Fe I is detected at a SNR of 14.5). We confirm previous observations of an asymmetry in Fe I absorption, but find no measurable ingress-egress asymmetry in Na I and Ca II. Together, these results suggest variations within different layers of the atmosphere of WASP-76 b: neutral metals such as Fe I trace deeper regions with stronger asymmetries, while Na I and Ca II probe regions higher in the atmosphere where the ingress-egress asymmetries are weaker. These findings provide new insights into the complex atmosphere of WASP-76 b and highlight the power of using KPF for atmospheric characterization. More broadly, the KPF SURFS-UP Survey will observe a large sample of UHJs, using transmission, emission, and phase-resolved spectroscopy to characterize their refractory abundances, upper atmospheres, and 3D dynamics.