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We present an analysis of microlensing event OGLE-2019-BLG-0825. This eventwas identified as a planetary candidate by preliminary modeling. We find thatsignificant residuals from the best-fit static binary-lens model exist and axallarap effect can fit the residuals very well and significantly improves$\chi^2$ values. On the other hand, by including the xallarap effect in ourmodels, we find that binary-lens parameters like mass-ratio, $q$, andseparation, $s$, cannot be constrained well. However, we also find that theparameters for the source system like the orbital period and semi major axisare consistent between all the models we analyzed. We therefore constrain theproperties of the source system better than the properties of the lens system.The source system comprises a G-type main-sequence star orbited by a browndwarf with a period of $P\sim5$ days. This analysis is the first to demonstratethat the xallarap effect does affect binary-lens parameters in planetaryevents. It would not be common for the presence or absence of the xallarapeffect to affect lens parameters in events with long orbital periods of thesource system or events with transits to caustics, but in other cases, such asthis event, the xallarap effect can affect binary-lens parameters.

OGLE-2019-BLG-0825: Constraints on the Source System and Effect on  Binary-lens Parameters arising from a Five Day Xallarap Effect in a Candidate  Planetary Microlensing Event