TOI-5126: a hot super-Neptune and warm Neptune pair discovered by TESS and CHEOPS

• Published in: Monthly notices of the Royal Astronomical Society Vol. 527; no. 3; pp. 8768 - 8783
• Main Authors: Fairnington, Tyler R, Nabbie, Emma, Huang, Chelsea X, Zhou, George, Foo, Orion, Millholland, Sarah, Wright, Duncan, Belinski, Alexandre A, Bieryla, Allyson, Ciardi, David R, Collins, Karen A, Collins, Kevin I, Everett, Mark, Howell, Steve B, Lissauer, Jack J, Lund, Michael B, Murgas, Felipe, Palle, Enric, Quinn, Samuel N, Relles, Howard M, Safonov, Boris S, Schwarz, Richard P, Scott, Nicholas J, Srdoc, Gregor, Ricker, George, Vanderspek, Roland, Seager, Sara, Latham, David W, Winn, Joshua W, Jenkins, Jon M, Bouma, Luke G, Shporer, Avi, Ting, Eric B, Dragomir, Diana, Kunimoto, Michelle, Eisner, Nora L
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 01-01-2024
• Subjects: Extrasolar planets; Free atmosphere; Gas giant planets; Neptune; Orbits; Photometry; Planet detection; Satellite observation; Transit; planets and satellites: detection; techniques: photometric; stars: individual TOI-5126
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stad3036

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.