TOI-1408: Discovery and Photodynamical Modeling of a Small Inner Companion to a Hot Jupiter Revealed by Transit Timing Variations
Ikuta, Kai; Latham, David W.; Quinn, Samuel N.; Cochran, William D.; Endl, Michael; Redfield, Seth; Knutson, Heather A.; García, Rafael A.; Kabáth, Petr; Collins, Karen A.; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Skarka, Marek; Bouy, Hervé; Shporer, Avi; Gandolfi, Davide; Nowak, Grzegorz; Albrecht, Simon; Cabrera, Juan; Fukui, Akihiko; Guenther, Eike W.; Hatzes, Artie P.; Korth, Judith; Narita, Norio; Persson, Carina M.; Van Eylen, Vincent; Mathur, Savita; MacQueen, Phillip J.; Deeg, Hans J.; Šubjak, Ján; Twicken, Joseph D.; Relles, Howard M.; Morales-Calderón, María; Barrado, David; Morello, Giuseppe; Beck, Paul G.; Palakkatharappil, Dinil B.; Livingston, John; Schwarz, Richard P.; Murgas, Felipe; Lillo-Box, Jorge; Martioli, Eder; Delfosse, Xavier; Carleo, Ilaria; Orell-Miquel, Jaume; Srdoc, Gregor; Pallé, Enric; Hébrard, Guillaume; Parviainen, Hannu; Chaturvedi, Priyanka; Watanabe, Noriharu; Hobbs, David; Boisse, Isabelle; Mustill, Alexander J.; Thomas, Luis; Kellermann, Hanna; Heidari, Neda; Greklek-McKeon, Michael; Stangret, Monika; Demangeon, Olivier; Osborne, Hanna L. M.; Pinter, Viktoria
Sweden, Germany, India, Spain, Italy, United States, Poland, France, Japan, Czech Republic, Denmark, Portugal, Brazil, United Kingdom, România, Croatia
Abstract
We report the discovery and characterization of a small planet, TOI-1408 c, on a 2.2 day orbit located interior to a previously known hot Jupiter, TOI-1408 b (P = 4.42 days, M = 1.86 ± 0.02 M Jup, R = 2.4 ± 0.5 R Jup) that exhibits grazing transits. The two planets are near 2:1 period commensurability, resulting in significant transit timing variations (TTVs) for both planets and transit duration variations for the inner planet. The TTV amplitude for TOI-1408 c is 15% of the planet's orbital period, marking the largest TTV amplitude relative to the orbital period measured to date. Photodynamical modeling of ground-based radial velocity (RV) observations and transit light curves obtained with the Transiting Exoplanet Survey Satellite and ground-based facilities leads to an inner planet radius of 2.22 ± 0.06 R ⊕ and mass of 7.6 ± 0.2 M ⊕ that locates the planet into the sub-Neptune regime. The proximity to the 2:1 period commensurability leads to the libration of the resonant argument of the inner planet. The RV measurements support the existence of a third body with an orbital period of several thousand days. This discovery places the system among the rare systems featuring a hot Jupiter accompanied by an inner low-mass planet.