HD 191939: Three Sub-Neptunes Transiting a Sun-like Star Only 54 pc Away

September 2020 • 2020AJ....160..113B

Authors • Badenas-Agusti, Mariona • Günther, Maximilian N. • Daylan, Tansu • Mikal-Evans, Thomas • Vanderburg, Andrew • Huang, Chelsea X. • Matthews, Elisabeth • Rackham, Benjamin V. • Bieryla, Allyson • Stassun, Keivan G. • Kane, Stephen R. • Shporer, Avi • Fulton, Benjamin J. • Hill, Michelle L. • Nowak, Grzegorz • Ribas, Ignasi • Pallé, Enric • Jenkins, Jon M. • Latham, David W. • Seager, Sara • Ricker, George R. • Vanderspek, Roland K. • Winn, Joshua N. • Abril-Pla, Oriol • Collins, Karen A. • Serra, Pere Guerra • Niraula, Prajwal • Rustamkulov, Zafar • Barclay, Thomas • Crossfield, Ian J. M. • Howell, Steve B. • Ciardi, David R. • Gonzales, Erica J. • Schlieder, Joshua E. • Caldwell, Douglas A. • Fausnaugh, Michael • McDermott, Scott • Paegert, Martin • Pepper, Joshua • Rose, Mark E. • Twicken, Joseph D.

Abstract • We present the discovery of three sub-Neptune-sized planets transiting the nearby and bright Sun-like star HD 191939 (TIC 269701147, TOI 1339), a Ks = 7.18 mag G8 V dwarf at a distance of only 54 pc. We validate the planetary nature of the transit signals by combining 5 months of data from the Transiting Exoplanet Survey Satellite with follow-up ground-based photometry, archival optical images, radial velocities, and high angular resolution observations. The three sub-Neptunes have similar radii ( ${R}_{{\rm{b}}}={3.42}_{-0.11}^{+0.11}$ , ${R}_{{\rm{c}}}={3.23}_{-0.11}^{+0.11}$ , and ${R}_{{\rm{d}}}={3.16}_{-0.11}^{+0.11}\,{R}_{\oplus }$ ), and their orbits are consistent with a stable, circular, and coplanar architecture near mean-motion resonances of 1:3 and 3:4 (Pb = 8.88, Pc = 28.58, and Pd = 38.35 days). The HD 191939 system is an excellent candidate for precise mass determinations of the planets with high-resolution spectroscopy due to the host star's brightness and low chromospheric activity. Moreover, the system's compact and near-resonant nature can provide an independent way to measure planetary masses via transit timing variations while also enabling dynamical and evolutionary studies. Finally, as a promising target for multiwavelength transmission spectroscopy of all three planets' atmospheres, HD 191939 can offer valuable insight into multiple sub-Neptunes born from a protoplanetary disk that may have resembled that of the early Sun.


IPAC Authors


David Ciardi

Senior Scientist


Benjamin Fulton

Assistant Scientist