Confirmation of Fe I on MASCARA-5 b's Dayside Observed With EXPRES

MASCARA-5 b/TOI-1431 b is an ultra-hot Jupiter [P orb=2.650237 plus or minus0.000003, d, T eq=2370 plus or minus70, K, M p=3.12 plus or minus0.18,M Jup, R p=1.49 plus or minus0.05,R Jup;][] addison2021 orbiting a bright Am star (V=8.0, mag). Recent time-series observations obtained with PEPSI@LBT during the planet's post-eclipse 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 pre-eclipse 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 5.5 sigma significance obtained from two nights of observations) and the fact that the thermal profile is inverted with lower and upper temperatures about2000, K and about4500, K, respectively. A search for Fe ii and Cr i did not yield any plausible detections. We also find that the pre-eclipse signal exhibits a non-negligible blueshift of-3.2 plus or minus1.4, km/s potentially caused by winds.