TOI-431/HIP 26013: a super-Earth and a sub-Neptune transiting a bright, early K dwarf, with a third RV planet
Henning, Thomas; Barclay, Thomas; Gorjian, Varoujan; Hellier, Coel; Latham, David W.; Jordán, Andrés; Espinoza, Néstor; Brahm, Rafael; Wheatley, Peter J.; Kane, Stephen R.; Stassun, Keivan G.; Bayliss, Daniel; Tan, Thiam-Guan; Smith, A. M. S.; Wittenmyer, Robert A.; Howell, Steve B.; Howard, Andrew W.; Petigura, Erik A.; Crossfield, Ian J. M.; Weiss, Lauren M.; Horner, Jonathan; Ziegler, Carl; Collins, Karen A.; Vanderspek, Roland; Winn, Joshua N.; Jenkins, Jon M.; Seager, S.; Sousa, S.; Figueira, P.; Günther, Maximilian N.; Shporer, Avi; Collins, Kevin I.; Dai, Fei; Fridlund, Malcolm; Henderson, Beth A.; Casewell, Sarah L.; Gill, Samuel; Goad, Michael R.; Anderson, David R.; Armstrong, David J.; Burleigh, Matthew R.; Dragomir, Diana; Jenkins, James S.; Lendl, Monika; McCormac, James; Osborn, Ares; Vines, Jose I.; West, Richard G.; Mann, Andrew W.; Stockdale, Chris; Jensen, Eric L. N.; Bowler, Brendan P.; Twicken, Joseph D.; Bryant, Edward M.; Batalha, Natalie; Matson, Rachel A.; Nielsen, Louise D.; Osborn, Hugh P.; Raynard, Liam; Plavchan, Peter; Barrado, David; Furlan, E.; Tanner, A.; Benneke, Björn; Gonzales, Erica J.; Scott, Nicholas J.; Schwarz, Richard P.; Matthews, Elisabeth C.; Sarkis, Paula; Fulton, Benjamin; Cale, Bryson; Tinney, C. G.; Ricker, George; Kielkopf, John; Okumura, Jack; Quintana, Elisa V.; Wright, Duncan J.; Zhang, Hui; Cloutier, Ryan; Law, Nicholas; Rose, Mark E.; Wang, Sharon X.; Robertson, Paul; Roy, Arpita; Briceño, César; Lillo-Box, Jorge; Díaz, Rodrigo F.; Burke, Christopher J.; Adibekyan, Vardan; Hojjatpanah, Saeed; Hoyer, Sergio; Dumusque, Xavier; Helled, Ravit; Santos, Nuno C.; Strøm, Paul A.; Udry, Stephane; Isaacson, Howard; Dressing, Courtney; Huber, Dan; Reefe, Michael; Demangeon, Olivier D. S.; Gaidos, E.; Bouchy, Francois; Pollacco, Don; Dorn, C.; Kidwell, Richard C.; Berberian, John; Addison, Brett C.; Mengel, Matthew W.; Acton, Jack S.; Tilbrook, Rosanna H.; Barros, Susana C. C.; Ballard, Sarah; Teske, J.; Santerne, Alexandre; Delgado Mena, E.; Morales, Farisa Y.; Ciardi, David; King, George W.; Cooke, Benjamin F.; Schlieder, J.; Villaseñor, Jesus Noel; Otegi, Jon; Hogan, Aleisha; Geneser, C.; Lund, M.; Stibbard, C.; Zohrabi, F.
United Kingdom, United States, Chile, Australia, Portugal, Netherlands, Sweden, Spain, Switzerland, Canada, Argentina, France, Germany, China
Abstract
We present the bright (Vmag = 9.12), multiplanet system TOI-431, characterized with photometry and radial velocities (RVs). We estimate the stellar rotation period to be 30.5 ± 0.7 d using archival photometry and RVs. Transiting Exoplanet Survey Satellite (TESS) objects of Interest (TOI)-431 b is a super-Earth with a period of 0.49 d, a radius of 1.28 ± 0.04 R⊕, a mass of 3.07 ± 0.35 M⊕, and a density of 8.0 ± 1.0 g cm-3; TOI-431 d is a sub-Neptune with a period of 12.46 d, a radius of 3.29 ± 0.09 R⊕, a mass of $9.90^{+1.53}_{-1.49}$ M⊕, and a density of 1.36 ± 0.25 g cm-3. We find a third planet, TOI-431 c, in the High Accuracy Radial velocity Planet Searcher RV data, but it is not seen to transit in the TESS light curves. It has an Msin i of $2.83^{+0.41}_{-0.34}$ M⊕, and a period of 4.85 d. TOI-431 d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterization, while the super-Earth TOI-431 b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431 b is a prime TESS discovery for the study of rocky planet phase curves.