TOI-2458 b: A mini-Neptune consistent with in situ hot Jupiter formation

January 2025 • 2025A&A...693A.235S

Authors • Šubjak, Ján • Gandolfi, Davide • Goffo, Elisa • Rapetti, David • Jankowski, Dawid • Mizuki, Toshiyuki • Dai, Fei • Serrano, Luisa M. • Wilson, Thomas G. • Goździewski, Krzysztof • Nowak, Grzegorz • Jenkins, Jon M. • Twicken, Joseph D. • Winn, Joshua N. • Bieryla, Allyson • Ciardi, David R. • Cochran, William D. • Collins, Karen A. • Deeg, Hans J. • García, Rafael A. • Guenther, Eike W. • Hatzes, Artie P. • Kabáth, Petr • Korth, Judith • Latham, David W. • Livingston, John H. • Lund, Michael B. • Mathur, Savita • Narita, Norio • Orell-Miquel, Jaume • Pallé, Enric • Persson, Carina M. • Redfield, Seth • Schwarz, Richard P. • Watanabe, David • Ziegler, Carl

Abstract • We report on the discovery and spectroscopic confirmation of TOI-2458 b, a transiting mini-Neptune around an F-type star leaving the main-sequence with a mass of M_★ = 1.05 ± 0.03 M_⊙, a radius of R_★ = 1.31 ± 0.03 R_⊙, an effective temperature of T_eff = 6005 ± 50 K, and a metallicity of ‑0.10 ± 0.05 dex. By combining TESS photometry with high-resolution spectra acquired with the HARPS spectrograph, we found that the transiting planet has an orbital period of ‑3.74 days, a mass of M_p = 13.31 ± 0.99 M_⊕ and a radius of R_p = 2.83 ± 0.20 R_⊕. The host star TOI-2458 shows a short activity cycle of ~54 days revealed in the HARPS S-index and Ha times series. We took the opportunity to investigate other F stars showing activity cycle periods comparable to that of TOI-2458 and found that they have shorter rotation periods than would be expected based on the gyrochronology predictions. In addition, we determined TOI-2458's stellar inclination angle to be i_* = 10.6_‑10.6^+13.3 degrees. We discuss that both phenomena (fast stellar rotation and planet orbit inclination) could be explained by in situ formation of a hot Jupiter interior to TOI-2458 b. It is plausible that this hot Jupiter was recently engulfed by the star. Analysis of HARPS spectra has identified the presence of another planet with a period of P = 16.55 ± 0.06 days and a minimum mass of M_p sin i = 10.22 ± 1.90 M_⊕. Using dynamical stability analysis, we constrained the mass of this planet to the range M_c ≃ (10, 25) M_⊕.

Links

• POSTSCRIPT https://www.aanda.org/10.1051/0004-6361/202451057/postscript
• PDF https://www.aanda.org/10.1051/0004-6361/202451057/pdf
• PREPRINT http://arxiv.org/abs/2409.17532
• ELECTR https://doi.org/10.1051%2F0004-6361%2F202451057