2025AJ....170..217V

Ground- and space-based observations have revealed that ultrahot Jupiters (UHJs, T_eq > 2200 K) typically have inverted thermal profiles, while cooler hot Jupiters have noninverted ones. This shift is theorized due to the onset of strong optical absorbers such as metal oxides (e.g., TiO, VO), metal hydrides (e.g. FeH), atomic species (e.g., Fe, Ti), and ions (e.g., H^–). High-resolution spectroscopy is valuable for characterizing the thermal, chemical, and dynamical atmospheric structures due to its sensitivity to detailed spectral line shapes. The newly commissioned WINERED high-resolution spectrograph (R ∼ 68,000) on the Magellan Clay 6.5 m telescope enhances capabilities with its high throughput in the J band (1.13-1.35 μm), capturing strong spectral features from key atmospheric species. In this study, we report detection of the dayside atmosphere of the UHJ WASP-189 b at a signal-to-noise ratio S/N ∼ 10, marking the first detection of an exoplanet atmosphere in emission with WINERED. Individually, we identify strong neutral iron (Fe) emission lines at S/N = 6.3, and tentatively detect neutral magnesium (Mg) and silicon (Si) at S/N > 4. Although not individually detected, we detect a combined set of trace species at S/N = 7.2, which is attributed mostly to neutral chromium (Cr) and aluminum (Al), alongside magnesium and silicon. These results help refine the understanding of key atmospheric species that influence the thermal structure of WASP-189 b and UHJs more broadly.