TOI-1431b/MASCARA-5b: A Highly Irradiated Ultra-Hot Jupiter Orbiting One of the Hottest & Brightest Known Exoplanet Host Stars

Abstract

We present the discovery of a highly irradiated and moderately inflated ultra-hot Jupiter, TOI-1431b/MASCARA-5b (HD 201033b), first detected by NASA's Transiting Exoplanet Survey Satellite mission (TESS) and the Multi-site All-Sky CAmeRA (MASCARA). The signal was established to be of planetary origin through radial velocity measurements obtained using SONG, SOPHIE, FIES, NRES, and EXPRES, which show a reflex motion of $K=294.1\pm 1.1$ m s${}^{-1}$. A joint analysis of the TESS and ground-based photometry and radial velocity measurements reveals that TOI-1431b has a mass of $M_p=3.12\pm 0.18$ ${\mathrm{M}}_{\mathrm{J}}$ ($990\pm 60$ M${}_{\oplus }$), an inflated radius of $R_p=1.49\pm 0.05$ ${\mathrm{R}}_{\mathrm{J}}$ ($16.7\pm 0.6$ R${}_{\oplus }$), and an orbital period of $P=2.650237\pm 0.000003$ d. Analysis of the spectral energy distribution of the host star reveals that the planet orbits a bright ($\mathrm{V}=8.049$ mag) and young ($0.29_{-0.19}^{+0.32}$ Gyr) Am type star with $T_{\mathrm{eff}}=7690_{-250}^{+400}$ $\mathrm{K}$, resulting in a highly irradiated planet with an incident flux of $⟨F⟩=7.24_{-0.64}^{+0.68}\times$10${}^9$ erg s${}^{-1}$ cm${}^{-2}$ ($5300_{-470}^{+500}{\mathrm{S}}_{\oplus }$) and an equilibrium temperature of $T_{eq}=2370\pm 70$ K. TESS photometry also reveals a secondary eclipse with a depth of $127_{-5}^{+4}$ppm as well as the full phase curve of the planet's thermal emission in the red-optical. This has allowed us to measure the dayside and nightside temperature of its atmosphere as $T_{\mathrm{day}}=3004\pm 64$ K and $T_{\mathrm{night}}=2583\pm 63$ K, the second hottest measured nightside temperature. The planet's low day/night temperature contrast ($\sim$420 K) suggests very efficient heat transport between the dayside and nightside hemispheres.

Accepted for publication in the Astronomical Journal. 39 pages, 18 figures, and 4 tables