Kavli Affiliate: Edward H. Morgan
| First 5 Authors: Samuel H. C. Cabot, Aaron Bello-Arufe, João M. Mendonça, René Tronsgaard, Ian Wong
| 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 ($T_{mathrm{eff}} simeq 7300$ 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$sigma$ 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 (${5.2sigma}$), 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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