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One of the most powerful methods used to estimate sky-projected spin-orbitangles of exoplanetary systems is through a spectroscopic transit observationknown as the Rossiter-McLaughlin (RM) effect. So far mostly single RMobservations have been used to estimate the spin-orbit angle, and thus therehave been no studies regarding the variation of estimated spin-orbit angle fromtransit to transit. Stellar activity can alter the shape of photometric transitlight curves and in a similar way they can deform the RM signal. In this paperwe discuss several RM observations, obtained using the HARPS spectrograph, ofknown transiting planets that all transit extremely active stars, and byanalyzing them individually we assess the variation in the estimated spin-orbitangle. Our results reveal that the estimated spin-orbit angle can varysignificantly (up to 42 degrees) from transit to transit, due to variation inthe configuration of stellar active regions over different nights. This findingis almost two times larger than the expected variation predicted fromsimulations. We could not identify any meaningful correlation between thevariation of estimated spin-orbit angles and the stellar magnetic activityindicators. We also investigated two possible approaches to mitigate thestellar activity influence on RM observations. The first strategy was based onobtaining several RM observations and folding them to reduce the stellaractivity noise. Our results demonstrated that this is a feasible and robust wayto overcome this issue. The second approach is based on acquiring simultaneoushigh-precision short-cadence photometric transit light curves usingTRAPPIST/SPECULOOS telescopes, which provide more information about the stellaractive region's properties and allow a better RM modeling.

Activity induced variation in spin-orbit angles as derived from Rossiter-McLaughlin measurements