TOI-257b (HD 19916b): A Warm sub-Saturn on a Moderately Eccentric Orbit Around an Evolved F-type Star

摘要: We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be planetary origin radial-velocity observations with Minerva-Australis telescope array. An analysis photometry, Minerva-Australis, FEROS, HARPS radial velocities, asteroseismic stellar oscillations reveals that has mass $M_P=0.134^{+0.023}_{-0.022}$$\rm{M_J}$ ($42.6^{+7.3}_{-7.0}$$\rm{M_{\oplus}}$), radius $R_P=0.626^{+0.013}_{-0.012}$$\rm{R_J}$ ($7.02^{+0.15}_{-0.13}$$\rm{R_{\oplus}}$), an orbit eccentricity $0.242^{+0.040}_{-0.065}$ period $18.38827\pm0.00072$$\rm{days}$. orbits bright ($\mathrm{V}=7.570$mag) somewhat evolved late F-type star $M_*=1.390\pm0.046$$\rm{M_{\odot}}$, $R_*=1.888\pm0.033$$\rm{R_{\odot}}$, $T_{\rm eff}=6075\pm90$$\rm{K}$, $v\sin{i}=11.3\pm0.5$km/s. Additionally, we statistically validate second non-transiting sub-Saturn planet $\sim71$day using velocity data. This system joins ranks small number exoplanet host stars have been characterized asteroseismology. Warm sub-Saturns are rare in known sample exoplanets, thus is important context future work studying formation migration history similar systems.