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 K_s = 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 (P_b = 8.88, P_c = 28.58, and P_d = 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.

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• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2020AJ....160..113B
• PDF https://iopscience.iop.org/article/10.3847/1538-3881/aba0b5/pdf
• PDF https://stacks.iop.org/1538-3881/160/113/pdf
• PREPRINT http://arxiv.org/abs/2002.03958
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2020AJ....160..113B
• DATA https://irsa.ipac.caltech.edu/bibdata/2020/B/2020AJ....160..113B.html
• ELECTR https://doi.org/10.3847%2F1538-3881%2Faba0b5
• DATA http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?type=REFERENCE&bibcode=2020arXiv200203958B