  One of the most powerful methods used to estimate sky-projected spin-orbit
angles of exoplanetary systems is through a spectroscopic transit observation
known as the Rossiter-McLaughlin (RM) effect. So far mostly single RM
observations have been used to estimate the spin-orbit angle, and thus there
have been no studies regarding the variation of estimated spin-orbit angle from
transit to transit. Stellar activity can alter the shape of photometric transit
light curves and in a similar way they can deform the RM signal. In this paper
we discuss several RM observations, obtained using the HARPS spectrograph, of
known transiting planets that all transit extremely active stars, and by
analyzing them individually we assess the variation in the estimated spin-orbit
angle. Our results reveal that the estimated spin-orbit angle can vary
significantly (up to 42 degrees) from transit to transit, due to variation in
the configuration of stellar active regions over different nights. This finding
is almost two times larger than the expected variation predicted from
simulations. We could not identify any meaningful correlation between the
variation of estimated spin-orbit angles and the stellar magnetic activity
indicators. We also investigated two possible approaches to mitigate the
stellar activity influence on RM observations. The first strategy was based on
obtaining several RM observations and folding them to reduce the stellar
activity noise. Our results demonstrated that this is a feasible and robust way
to overcome this issue. The second approach is based on acquiring simultaneous
high-precision short-cadence photometric transit light curves using
TRAPPIST/SPECULOOS telescopes, which provide more information about the stellar
active region's properties and allow a better RM modeling.
