# PEPSI Investigation, Retrieval, and Atlas of Numerous Giant Atmospheres (PIRANGA). IV. High-resolution Phased-resolved Spectroscopy of the Ultra-hot-Jupiter KELT-20 b

## TL;DR

This study uses high-resolution spectroscopy to analyze the atmosphere of the ultra-hot-Jupiter KELT-20 b, revealing temperature differences and chemical abundances on its day and night sides.

## Contribution

The paper provides the first measurements of Ni and Ca abundances in emission for KELT-20 b and compares chemical abundance ratios across different atmospheric regions.

## Key findings

- Abundance ratios [Ni/Fe] and [Ca/Fe] are consistent with solar values within 2σ.
- The evening side of KELT-20 b is hotter than the morning side by ∼100 K.
- Chemical abundance ratios remain relatively constant despite significant phase-dependent abundance variations.

## Abstract

We present five datasets of high-resolution optical emission spectra of the
ultra-hot-Jupiter KELT-20 b with the PEPSI spectrograph. Using a Bayesian
retrieval framework, we constrain its dayside pressure–temperature profile and
abundances of Fe, Ni, and Ca, providing the first measurements for Ni and Ca for
KELT-20 b in emission. We retrieve the preeclipse and posteclipse datasets
separately (corresponding to the evening and morning sides, respectively), and
compare the constraints on their thermal structures and chemical abundances. We
constrain lower abundances in the pre-eclipse datasets compared to the
posteclipse datasets. We interpret these results with an equilibrium chemistry
model which suggests ∼10–30× supersolar refractory abundances. Due to the
well-known degeneracy between absolute abundances and continuum opacities, the
abundance ratios are more precise probes of the planetary abundances. Therefore
we measure the abundance ratios [Ni/Fe] and [Ca/Fe] across these datasets and
find they agree within 1σ. We constrain [Ni/Fe] to
be consistent with solar within 2σ, and [Ca/Fe] to
be 0.001–0.01× solar, not accounting for ionization. We compare these abundance
ratios with literature results for KELT-20 b in transmission, and find they
agree within 2σ, suggesting that even though the
abundances vary significantly as a function of phase, the abundance ratios of
these species remain relatively constant. We find a ∼100 K difference in
temperature at the top of the thermal inversion, suggesting a hotter evening
side than morning side and underscoring the importance of considering 3D effects
when studying ultrahot Jupiters.