TOI-2458 b: A mini-Neptune consistent with in situ hot Jupiter formation
/ Authors
J. vSubjak, D. Gandolfi, E. Goffo, D. Rapetti, D. Jankowski, Toshiyuki Mizuki, F. Dai, L. Serrano, Thomas G. Wilson, Krzysztof Go'zdziewski
and 26 more authors
G. Nowak, J. Jenkins, J. Twicken, J. Winn, A. Bieryla, D. Ciardi, W. Cochran, K. Collins, H. Deeg, Rafael A. Garc'ia, E. Guenther, A. Hatzes, P. Kab'ath, J. Korth, D. Latham, J. Livingston, M. Lund, S. Mathur, N. Narita, J. Orell-Miquel, E. Pall'e, C. Persson, S. Redfield, R. Schwarz, D. Watanabe, C. Ziegler
/ 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_ odot $, a radius of $R_ odot $, an effective temperature of $T_ eff and a metallicity of $-0.10 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 oplus $ and a radius of $R_p=2.83 oplus $. The host star TOI-2458 shows a short activity cycle of sim 54\,days revealed in the HARPS S-index and Halpha 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_ $\,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 and a minimum mass of $M_p i=10.22 oplus $. Using dynamical stability analysis, we constrained the mass of this planet to the range $M_ c oplus
Journal: Astronomy & Astrophysics