1. TOI-2458 b: A mini-Neptune consistent with in situ hot Jupiter formation
- Author
-
Šubjak, Ján, Gandolfi, Davide, Goffo, Elisa, Rapetti, David, Nowak, Grzegorz, Mizuki, Toshiyuki, Dai, Fei, Serrano, Luisa M., Wilson, Thomas G., Jankowski, Dawid, Goździewski, Krzysztof, Jenkins, Jon M., Twicken, Joseph D., Winn, Joshua N., Bieryla, Allyson, 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., Mathur, Savita, Narita, Norio, Orell-Miquel, Jaume, Pallé, Enric, Persson, Carina M., Redfield, Seth, Schwarz, Richard P., Watanabe, David, and Ziegler, Carl
- Subjects
Astrophysics - Earth and Planetary Astrophysics - 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 $M_\star=1.05 \pm 0.03$ M$_{\odot}$, a radius of $R_\star=1.31 \pm 0.03$ R$_{\odot}$, an effective temperature of $T_{\rm eff}=6005\pm50$ K, and a metallicity of $-0.10\pm0.05$ 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 $\sim$3.74 days, a mass of $M_p=13.31\pm0.99$ M$_{\oplus}$ and a radius of $R_p=2.83\pm0.20$ R$_{\oplus}$. The host star TOI-2458 shows a short activity cycle of $\sim$54 days revealed in the HARPS S-index time 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 $i_\star\,=\,10.6_{-10.6}^{+13.3}$ 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 $P\,=\,16.55\pm0.06$ days and a minimum mass of $M_p \sin i=10.22\pm1.90$ M$_{\oplus}$., Comment: 22 pages, 17 figures, submitted to Astronomy & Astrophysics
- Published
- 2024