The Transiting Exoplanet Survey Satellite ( TESS ) is performing a near all-sky survey for planets that transit bright stars .
In addition , its excellent photometric precision enables asteroseismology of solar-type and red-giant stars , which exhibit convection-driven , solar-like oscillations .
Simulations predict that TESS will detect solar-like oscillations in nearly 100 stars already known to host planets .
In this paper , we present an asteroseismic analysis of the known red-giant host stars HD 212771 and HD 203949 , both systems having a long-period planet detected through radial velocities .
These are the first detections of oscillations in previously known exoplanet-host stars by TESS , further showcasing the mission ’ s potential to conduct asteroseismology of red-giant stars .
We estimate the fundamental properties of both stars through a grid-based modeling approach that uses global asteroseismic parameters as input .
We discuss the evolutionary state of HD 203949 in depth and note the large discrepancy between its asteroseismic mass ( M _ { \ast } = 1.23 \pm 0.15 { M } _ { \odot } if on the red-giant branch or M _ { \ast } = 1.00 \pm 0.16 { M } _ { \odot } if in the clump ) and the mass quoted in the discovery paper ( M _ { \ast } = 2.1 \pm 0.1 { M } _ { \odot } ) , implying a change > 30 \% in the planet ’ s mass .
Assuming HD 203949 to be in the clump , we investigate the planet ’ s past orbital evolution and discuss how it could have avoided engulfment at the tip of the red-giant branch .
Finally , HD 212771 was observed by K2 during its Campaign 3 , thus allowing for a preliminary comparison of the asteroseismic performances of TESS and K2 .
We estimate the ratio of the observed oscillation amplitudes for this star to be A _ { max } ^ { TESS } / A _ { max } ^ { K 2 } = 0.75 \pm 0.14 , consistent with the expected ratio of \sim 0.85 due to the redder bandpass of TESS .