TOI-431/HIP 26013: A super-Earth and a sub-Neptune transiting a bright, early K dwarf, with a third RV planet
Creators: name: Twicken, J.D.
name: Burke, C.J.
name: Santos, N.C.
name: Wheatley, P.J.
name: Kidwell, R.C.
name: King, G.W.
name: Mengel, M.W.
name: Cloutier, R.
name: Adibekyan, V.
name: Díaz, R.F.
name: Kane, S.R.
name: Hellier, C.
name: Armstrong, D.J.
name: Osborn, A.
name: Batalha, N.
name: Bryant, E.M.
name: Kielkopf, J.
name: Jordán, A.
name: Demangeon, O.D.S.
name: Dai, F.
name: Wittenmyer, R.A.
name: Gill, S.
name: Villaseñor, J.N.
name: Petigura, E.A.
name: Dorn, C.
name: Cooke, B.F.
name: Tilbrook, R.H.
name: Gorjian, V.
name: Winn, J.N.
name: Brahm, R.
name: Lund, M.
name: Osborn, H.P.
name: Helled, R.
name: Mann, A.W.
name: Zohrabi, F.
name: Strøm, P.A.
name: Gonzales, E.J.
name: Rose, M.E.
name: Reefe, M.
name: Ballard, S.
name: Casewell, S.L.
name: Barros, S.C.C.
name: Collins, K.I.
name: Latham, D.W.
name: Roy, A.
name: Fridlund, M.
name: Lillo-Box, J.
name: Vanderspek, R.
name: Jenkins, J.S.
name: Seager, S.
name: Ricker, G.
name: Matson, R.A.
name: Schlieder, J.
name: Lendl, M.
name: Stassun, K.G.
name: Zhang, H.
name: Santerne, A.
name: Geneser, C.
name: Udry, S.
name: Teske, J.
name: Nielsen, L.D.
name: Stockdale, C.
name: Ziegler, C.
name: Robertson, P.
name: Plavchan, P.
name: Gaidos, E.
name: Okumura, J.
name: West, R.G.
name: Furlan, E.
name: Sousa, S.
name: Anderson, D.R.
name: Burleigh, M.R.
name: Günther, M.N.
name: Matthews, E.C.
name: Otegi, J.
name: Raynard, L.
name: Barrado, D.
name: Delgado Mena, E.
name: Collins, K.A.
name: Fulton, B.
name: Bouchy, F.
name: Dumusque, X.
name: Hoyer, S.
name: Smith, A.M.S.
name: Briceño, C.
name: Barclay, T.
name: Hojjatpanah, S.
name: Howard, A.W.
name: McCormac, J.
name: Shporer, A.
name: Tinney, C.G.
name: Bowler, B.P.
name: Tanner, A.
name: Weiss, L.M.
name: Stibbard, C.
name: Scott, N.J.
name: Horner, J.
name: Espinoza, N.
name: Wang, S.X.
name: Tan, T.-G.
name: Schwarz, R.P.
name: Ciardi, D.
name: Morales, F.Y.
name: Figueira, P.
name: Vines, J.I.
name: Berberian, J., Jr.
name: Dressing, C.
name: Howell, S.B.
name: Addison, B.C.
name: Cale, B.
name: Jenkins, J.M.
name: Law, N.
name: Bayliss, D.
name: Hogan, A.
name: Acton, J.S.
name: Benneke, B.
name: Crossfield, I.J.M.
name: Goad, M.R.
name: Isaacson, H.
name: Dragomir, D.
name: Jensen, E.L.N.
name: Quintana, E.V.
name: Henning, T.
name: Sarkis, P.
name: Wright, D.J.
name: Huber, D.
name: Henderson, B.A.
name: Pollacco, D.
Publisher: name: Oxford University Press
Year: 2021

description: 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.