Deviations in the astrometric observable for the S2 star caused by the different photon propagation alone (i.e., not considering modifications to the star’s orbit) in theories with values of γ that differ from the general relativistic case (γ = 1). A variation in γ on the order of 100% from the general relativistic case produces an astrometric deviation that is below the instrumental sensitivity of GRAVITY, at 10 µas.