Confirmation of Feion MASCARA-5 b’s Dayside Observed With EXPRES

MASCARA-5 b/TOI-1431 b is an ultra-hot Jupiter (P_orb = 2.650237 ± 0.000003 dayd, T_eq = 2370 ± 70 K, M_p = 3.12 ± 0.18 M_Jup, R_p = 1.49 ± 0.05 R_Jup) orbiting a bright Am star (V = 8.0 mag). Recent time-series observations obtained with PEPSI@LBT during the planet’s posteclipse phases have revealed Fe i emission lines indicative of a thermally inverted atmosphere. These observations demonstrate that MASCARA-5 b is well suited to atmospheric characterization via emission spectroscopy, thereby motivating further follow-up observations covering additional orbital phases to constrain the planet’s atmospheric chemistry, thermal structure, and dynamics. Here we present preeclipse time-series observations obtained with the high-resolution optical spectrograph EXPRES@LDT. Our analysis confirms the previous detection of gas-phase Fe i on MASCARA-5 b’s dayside (with a 5.5σ significance obtained from two nights of observations), and the fact that the thermal profile is inverted with lower and upper temperatures ∼2000 K and ∼4500 K, respectively. A search for Fe ii and Cr i did not yield any plausible detections. We also find that the preeclipse signal exhibits a nonnegligible blueshift of −3.2 ± 1.4 km s⁻¹ potentially caused by winds.