Close-in , massive exoplanets raise significant tides in their stellar hosts .
We compute the radial velocity ( RV ) signal due to this fluid motion in the equilibrium tide approximation .
The predicted radial velocities in the observed sample of exoplanets exceed 1 m / s for 17 systems , with the largest predicted signal being \sim 30 m s ^ { -1 } for WASP-18 b. Tidally-induced RV ’ s are thus detectable with present methods .
Both tidal fluid flow and the epicyclic motion of a slightly eccentric orbit produce an RV signal at twice the orbital frequency .
If care is not taken , the tidally induced RV may , in some cases , be confused with a finite orbital eccentricity .
Indeed , WASP-18 b is reported to have an eccentric orbit with small e = 0.009 and pericenter longitude \omega = - \pi / 2 .
Whereas such a close alignment of the orbit and line of sight to the observer requires fine tuning , this phase in the RV signal is naturally explained by the tidal velocity signature of an e = 0 orbit .
Additionally , the equilibrium tide estimate for the amplitude is in rough agreement with the data .
Thus the reported eccentricity for WASP-18 b is instead likely a signature of the tidally-induced RV in the stellar host .
Measurement of both the orbital and tidal velocity for non-transiting planets may allow planet mass and inclination to be separately determined solely from radial velocity data .
We suggest that high precision fitting of RV data should include the tidal velocity signal in those cases where it may affect the determination of orbital parameters .