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

Addison, Brett C.; Knudstrup, Emil; Wong, Ian; Hébrard, Guillaume; Dorval, Patrick; Snellen, Ignas; Albrecht, Simon; Bello-Arufe, Aaron; Almenara, Jose-Manuel; Boisse, Isabelle; Bonfils, Xavier; Dalal, Shweta; Demangeon, Olivier D. S.; Hoyer, Sergio; Kiefer, Flavien; Santos, N. C.; Nowak, Grzegorz; Luque, Rafael; Stangret, Monika; Palle, Enric; Tronsgaard, René; Antoci, Victoria; Buchhave, Lars A.; Günther, Maximilian N.; Daylan, Tansu; Murgas, Felipe; Parviainen, Hannu; Esparza-Borges, Emma; Crouzet, Nicolas; Narita, Norio; Fukui, Akihiko; Kawauchi, Kiyoe; Watanabe, Noriharu; Rabus, Markus; Johnson, Marshall C.; Otten, Gilles P. P. L.; Jan Talens, Geert; Cabot, Samuel H. C.; Fischer, Debra A.; Grundahl, Frank; Fredslund Andersen, Mads; Jessen-Hansen, Jens; Pallé, Pere; Shporer, Avi; Ciardi, David R.; Clark, Jake T.; Wittenmyer, Robert A.; Wright, Duncan J.; Horner, Jonathan; Collins, Karen A.; Jensen, Eric L. N.; Kielkopf, John F.; Schwarz, Richard P.; Srdoc, Gregor; Yilmaz, Mesut; Senavci, Hakan Volkan; Diamond, Brendan; Harbeck, Daniel; Komacek, Thaddeus D.; Smith, Jeffrey C.; Wang, Songhu; Eastman, Jason D.; Stassun, Keivan G.; Latham, David W.; Vanderspek, Roland; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Louie, Dana R.; Bouma, Luke G.; Twicken, Joseph D.; Levine, Alan M.; McLean, Brian
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The Astronomical Journal

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We present the discovery of a highly irradiated and moderately inflated ultrahot Jupiter, TOI-1431b/MASCARA-5 b (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 ± 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 ± 0.18 M J (990 ± 60 M ⊕), an inflated radius of R p = 1.49 ± 0.05 R J (16.7 ± 0.6 R ⊕), and an orbital period of P = 2.650237 ± 0.000003 days. Analysis of the spectral energy distribution of the host star reveals that the planet orbits a bright (V = 8.049 mag) and young ( ${0.29}_{-0.19}^{+0.32}$ Gyr) Am type star with ${T}_{\mathrm{eff}}={7690}_{-250}^{+400}$ K, resulting in a highly irradiated planet with an incident flux of $\langle F\rangle ={7.24}_{-0.64}^{+0.68}\times $ 109 erg s-1 cm-2 ( ${5300}_{-470}^{+500}\,{S}_{\oplus }$ ) and an equilibrium temperature of T eq = 2370 ± 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 day = 3004 ± 64 K and T night = 2583 ± 63 K, the second hottest measured nightside temperature. The planet's low day/night temperature contrast (~420 K) suggests very efficient heat transport between the dayside and nightside hemispheres. Given the host star brightness and estimated secondary eclipse depth of ~1000 ppm in the K band, the secondary eclipse is potentially detectable at near-IR wavelengths with ground-based facilities, and the planet is ideal for intensive atmospheric characterization through transmission and emission spectroscopy from space missions such as the James Webb Space Telescope and the Atmospheric Remote-sensing Infrared Exoplanet Large-survey.
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