HD 21520 b: a warm sub-Neptune transiting a bright G dwarf

November 2024 • 2024MNRAS.534.3744N

Authors • Nies, Molly • Mireles, Ismael • Bouchy, François • Dragomir, Diana • Nicholson, Belinda A. • Eisner, Nora L. • Sousa, Sergio G. • Collins, Karen A. • Howell, Steve B. • Ziegler, Carl • Hellier, Coel • Addison, Brett • Ballard, Sarah • Bowler, Brendan P. • Briceño, César • Clark, Catherine A. • Conti, Dennis M. • Dumusque, Xavier • Edwards, Billy • Gnilka, Crystal L. • Hobson, Melissa • Horner, Jonathan • Kane, Stephen R. • Kielkopf, John • Lavie, Baptiste • Law, Nicholas • Lendl, Monika • Littlefield, Colin • Liu, Huigen • Mann, Andrew W. • Mengel, Matthew W. • Oddo, Dominic • Okumura, Jack • Palle, Enric • Plavchan, Peter • Psaridi, Angelica • Santos, Nuno C. • Schwarz, Richard P. • Shporer, Avi • Wittenmyer, Robert A. • Wright, Duncan J. • Zhang, Hui • Watanabe, David • Medina, Jennifer V. • Villaseñor, Joel • Ting, Eric B. • Christiansen, Jessie L. • Winn, Joshua N. • Stassun, Keivan G. • Seager, S. • Latham, David W. • Ricker, George R.

Abstract • We report the discovery and validation of HD 21520 b, a transiting planet found with Transiting Exoplanet Survey Satellite and orbiting a bright G dwarf (V = 9.2, $T_{\rm eff} = 5871 \pm 62$ K, $R_{\star } = 1.04\pm 0.02\, {\rm R}_{\odot }$). HD 21520 b was originally alerted as a system (TOI-4320) consisting of two planet candidates with periods of 703.6 and 46.4 d. However, our analysis supports instead a single-planet system with an orbital period of $25.1292\pm 0.0001$ d and radius of $2.70 \pm 0.09\, {\rm R}_{{\oplus }}$. Three full transits in sectors 4, 30, and 31 match this period and have transit depths and durations in agreement with each other, as does a partial transit in sector 3. We also observe transits using CHEOPS and LCOGT. SOAR and Gemini high-resolution imaging do not indicate the presence of any nearby companions, and MINERVA-Australis and CORALIE radial velocities rule out an on-target spectroscopic binary. Additionally, we use ESPRESSO radial velocities to obtain a tentative mass measurement of $7.9^{+3.2}_{-3.0}\, {\rm M}_{{\oplus }}$, with a 3$\sigma$ upper limit of 17.7 ${\rm M}_{{\oplus }}$. Due to the bright nature of its host and likely significant gas envelope of the planet, HD 21520b is a promising candidate for further mass measurements and for atmospheric characterization.

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• PDF https://academic.oup.com/mnras/pdf-lookup/doi/10.1093/mnras/stae2079
• ELECTR https://doi.org/10.1093%2Fmnras%2Fstae2079
• PREPRINT http://arxiv.org/abs/2406.09595