TOI-5126: a hot super-Neptune and warm Neptune pair discovered by TESS and CHEOPS
Bieryla, Allyson; Latham, David W.; Quinn, Samuel N.; Zhou, George; Howell, Steve B.; Lissauer, Jack J.; Collins, Karen A.; Vanderspek, Roland; Seager, Sara; Jenkins, Jon M.; Shporer, Avi; Collins, Kevin I.; Ciardi, David R.; Palle, Enric; Dragomir, Diana; Lund, Michael B.; Huang, Chelsea X.; Relles, Howard M.; Ting, Eric B.; Kunimoto, Michelle; Bouma, Luke G.; Scott, Nicholas J.; Schwarz, Richard P.; Murgas, Felipe; Wright, Duncan; Ricker, George; Everett, Mark; Nabbie, Emma; Srdoc, Gregor; Millholland, Sarah; Eisner, Nora L.; Safonov, Boris S.; Belinski, Alexandre A.; Fairnington, Tyler R.; Foo, Orion; Winn, Joshua W.
Australia, United States, Russia, Spain, Croatia
Abstract
We present the confirmation of a hot super-Neptune with an exterior Neptune companion orbiting a bright (V = 10.1 mag) F-dwarf identified by the Transiting Exoplanet Survey Satellite (TESS). The two planets, observed in sectors 45, 46, and 48 of the TESS extended mission, are $4.74_{-0.14}^{+0.16}$ and $3.86_{-0.16}^{+0.17}$ R⊕ with $5.4588385_{-0.0000072}^{+0.0000070}$ and $17.8999_{-0.0013}^{+0.0018}$ d orbital periods, respectively. We also obtained precise space-based photometric follow-up of the system with ESA's CHaracterising ExOplanets Satellite to constrain the radius and ephemeris of TOI-5126 b. TOI-5126 b is located in the 'hot Neptune Desert' and is an ideal candidate for follow-up transmission spectroscopy due to its high-predicted equilibrium temperature (Teq = ${1442}_{-40}^{+46}$ K) implying a cloud-free atmosphere. TOI-5126 c is a warm Neptune (Teq = $971_{-27}^{+31}$ K) also suitable for follow-up. Tentative transit timing variations have also been identified in analysis, suggesting the presence of at least one additional planet, however this signal may be caused by spot-crossing events, necessitating further precise photometric follow-up to confirm these signals.