TOI-2109b: An Ultrahot Gas Giant on a 16 hr Orbit
Creators: name: Wong, Ian
name: Shporer, Avi
name: Zhou, George
name: Kitzmann, Daniel
name: Komacek, Thaddeus D.
name: Tan, Xianyu
name: Tronsgaard, René
name: Buchhave, Lars A.
name: Vissapragada, Shreyas
name: Greklek-McKeon, Michael
name: Rodriguez, Joseph E.
name: Ahlers, John P.
name: Quinn, Samuel N.
name: Furlan, Elise
name: Howell, Steve B.
name: Bieryla, Allyson
name: Heng, Kevin
name: Knutson, Heather A.
name: Collins, Karen A.
name: McLeod, Kim K.
name: Berlind, Perry
name: Brown, Peyton
name: Calkins, Michael L.
name: de Leon, Jerome P.
name: Esparza-Borges, Emma
name: Esquerdo, Gilbert A.
name: Fukui, Akihiko
name: Gan, Tianjun
name: Girardin, Eric
name: Gnilka, Crystal L.
name: Ikoma, Masahiro
name: Jensen, Eric L. N.
name: Kielkopf, John
name: Kodama, Takanori
name: Kurita, Seiya
name: Lester, Kathryn V.
name: Lewin, Pablo
name: Marino, Giuseppe
name: Murgas, Felipe
name: Narita, Norio
name: Pallé, Enric
name: Schwarz, Richard P.
name: Stassun, Keivan G.
name: Tamura, Motohide
name: Watanabe, Noriharu
name: Benneke, Björn
name: Ricker, George R.
name: Latham, David W.
name: Vanderspek, Roland
name: Seager, Sara
name: Winn, Joshua N.
name: Jenkins, Jon M.
name: Caldwell, Douglas A.
name: Fong, William
name: Huang, Chelsea X.
name: Mireles, Ismael
name: Schlieder, Joshua E.
name: Shiao, Bernie
name: Villaseñor, Jesus Noel
Publisher: name: arXiv
Year: 2021
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We report the discovery of an ultrahot Jupiter with an extremely short orbital period of $0.67247414\,\pm\,0.00000028$ days ($\sim$16 hr). The $1.347 \pm 0.047$ $R_{\rm Jup}$ planet, initially identified by the Transiting Exoplanet Survey Satellite (TESS) mission, orbits TOI-2109 (TIC 392476080): a $T_{\rm eff} \sim 6500$ K F-type star with a mass of $1.447 \pm 0.077$ $M_{\rm Sun}$, a radius of $1.698 \pm 0.060$ $R_{\rm Sun}$, and a rotational velocity of $v\sin i_* = 81.9 \pm 1.7$ km s$^{-1}$. The planetary nature of TOI-2109b was confirmed through radial velocity measurements, which yielded a planet mass of $5.02 \pm 0.75$ $M_{\rm Jup}$. Analysis of the Doppler shadow in spectroscopic transit observations indicates a well-aligned system, with a sky-projected obliquity of $λ= 1\overset{\circ}{.}7 \pm 1\overset{\circ}{.}7$. From the TESS full-orbit light curve, we measured a secondary eclipse depth of $731 \pm 46$ ppm, as well as phase-curve variations from the planet's longitudinal brightness modulation and ellipsoidal distortion of the host star. Combining the TESS-band occultation measurement with a $K_s$-band secondary eclipse depth ($2012 \pm 80$ ppm) derived from ground-based observations, we find that the dayside emission of TOI-2109b is consistent with a brightness temperature of $3631 \pm 69$ K, making it the second hottest exoplanet hitherto discovered. By virtue of its extreme irradiation and strong planet-star gravitational interaction, TOI-2109b is an exceptionally promising target for intensive follow-up studies using current and near-future telescope facilities to probe for orbital decay, detect tidally driven atmospheric escape, and assess the impacts of H$_2$ dissociation and recombination on the global heat transport.
description: 30 pages, 17 figures, published in AJ