TOI-1431b/MASCARA-5b: A Highly Irradiated Ultrahot Jupiter Orbiting One of the Hottest and Brightest Known Exoplanet Host Stars
Authors: 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 
Published: December 2021

Abstract
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

eff

=

7690

−
250

+
400

K, resulting in a highly irradiated planet with an incident flux of

〈
F
〉
=

7.24

−
0.64

+
0.68

×

109 erg s−1 cm−2 (

5300

−
470

+
500

S

⊕

) 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.