Kavli Affiliate: Edward Morgan
| Summary:
We present the discovery of TOI-1518b — an ultra-hot Jupiter orbiting a bright star $V = 8.95$. The transiting planet is confirmed using high-resolution optical transmission spectra from EXPRES. It is inflated, with $R_p = 1.875pm0.053,R_rm J$, and exhibits several interesting properties, including a misaligned orbit ($240.34^+0.93_-0.98$ degrees) and nearly grazing transit ($b =0.9036^+0.0061_-0.0053$). The planet orbits a fast-rotating F0 host star ($T_mathrmeff simeq 7300$ K) in 1.9 days and experiences intense irradiation. Notably, the TESS data show a clear secondary eclipse with a depth of $364pm28$ ppm and a significant phase curve signal, from which we obtain a relative day-night planetary flux difference of roughly 320 ppm and a 5.2$σ$ detection of ellipsoidal distortion on the host star. Prompted by recent detections of atomic and ionized species in ultra-hot Jupiter atmospheres, we conduct an atmospheric cross-correlation analysis. We detect neutral iron ($5.2σ$), at $K_p = 157^+68_-44$ km s$^-1$ and $V_rm sys = -16^+2_-4$ km s$^-1$, adding another object to the small sample of highly irradiated gas-giant planets with Fe detections in transmission. Detections so far favor particularly inflated gas giants with radii $gtrsim 1.78,R_rm J$; although this may be due to observational bias. With an equilibrium temperature of $T_rm eq=2492pm38$ K and a measured dayside brightness temperature of $3237pm59$ K (assuming zero geometric albedo), TOI-1518b is a promising candidate for future emission spectroscopy to probe for a thermal inversion.
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