TOI-431/HIP 26013: a super-Earth and a sub-Neptune transiting a bright, early K dwarf, with a third RV planet
Ares Osborn, D. J. Armstrong, Bryson Cale, Rafael Brahm, Robert A. Wittenmyer, Fei Dai, Ian J. M. Crossfield, Edward M. Bryant, V. Adibekyan, Ryan Cloutier, Karen A. Collins, E. Delgado Mena, M. Fridlund, C. Hellier, Steve B. Howell, George W. King, J. Lillo-Box, Jon Otegi, S. G. Sousa, Keivan G. Stassun, Elisabeth C. Matthews, Carl Ziegler, G. Ricker, R. Vanderspek, David W. Latham, Sara Seager, Joshua N. Winn, Jon M. Jenkins, Jack S Acton, Brett Addison, D. R. Anderson, Sarah Ballard, D. Barrado, S. C. C. Barros, Natalie M. Batalha, Daniel Bayliss, Thomas Barclay, Björn Benneke, John Berberian, F. Bouchy, Brendan P. Bowler, César Briceño, Christopher J. Burke, M. R. Burleigh, S. L. Casewell, David R. Ciardi, Kevin I. Collins, Benjamin F Cooke, O. D. S. Demangeon, R. F. Díaz, Caroline Dorn, Diana Dragomir, Courtney D. Dressing, X. Dumusque, Néstor Espinoza, P. Figueira, Benjamin J. Fulton, Elise Furlan, Eric Gaidos, Claire Geneser, Samuel Gill, M. R. Goad, Erica J. Gonzales, Varoujan Gorjian, Maximilian N. Günther, Ravit Helled, Beth A Henderson, Thomas Henning, Aleisha Hogan, S. Hojjatpanah, Jonathan Horner, Andrew W. Howard, S. Hoyer, Daniel Huber, Howard Isaacson, J. S. Jenkins, Eric L. N. Jensen, Andrés Jordán, Stephen R. Kane, Richard C. Kidwell, John F. Kielkopf, Nicholas M. Law, M. Lendl, Mikkel N. Lund, Rachel A. Matson, Andrew W. Mann, J. McCormac, Matthew W. Mengel, Farisa Y. Morales, Louise D. Nielsen, Jack Okumura, H. P. Osborn, Erik A. Petigura, Peter Plavchan, D. Pollacco, Elisa V. Quintana, Liam Raynard, Paul Robertson, Mark E. Rose, Arpita Roy
Abstract
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.