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The Transiting Exoplanet Survey Satellite (TESS) is observing bright knownplanet-host stars across almost the entire sky. These stars have been subjectto extensive ground-based observations, providing a large number of radialvelocity (RV) measurements. In this work we use the new TESS photometricobservations to characterize the star $\lambda^2$ Fornacis, and following thisto update the parameters of the orbiting planet $\lambda^2$ For b. We measurethe p-mode oscillation frequencies in $\lambda^2$ For, and in combination withnon-seismic parameters estimate the stellar fundamental properties usingstellar models. Using the revised stellar properties and a time series ofarchival RV data from the UCLES, HIRES and HARPS instruments spanning almost 20years, we refit the orbit of $\lambda^2$ For b and search the RV residuals forremaining variability. We find that $\lambda^2$ For has a mass of$1.16\pm0.03$M$_\odot$ and a radius of $1.63\pm0.04$R$_\odot$, with an age of$6.3\pm0.9$Gyr. This and the updated RV measurements suggest a mass of$\lambda^2$ For b of $16.8^{+1.2}_{-1.3}$M$_\oplus$, which is $\sim5$M$_\oplus$less than literature estimates. We also detect a periodicity at 33 days in theRV measurements, which is likely due to the rotation of the host star. Whileprevious literature estimates of the properties of $\lambda^2$ are ambiguous,the asteroseismic measurements place the star firmly at the early stage of itssubgiant evolutionary phase. Typically only short time series of photometricdata are available from TESS, but by using asteroseismology it is stillpossible to provide tight constraints on the properties of bright stars thatuntil now have only been observed from the ground. This prompts a reexaminationof archival RV data from the past few decades to update the characteristics ofthe planet hosting systems observed by TESS for which asteroseismology ispossible.

Tess asteroseismology of the known planet host star $\lambda^2$ Fornacis