Average of the residuals in the difference image between the original and the symmetrized image of the NSC vs. the value of the tilt angle θ used to symmetrize the image. Panel a: average of the residuals for stars with 12.5 <  K_s, extc <  14.0. We find a minimum at θ = −5° that is not very significant. Panel b: average of the residuals for stars with 9.0 <  K_s, extc <  12.0. We find a minimum for θ = −6°. Panel c: average of the residuals for stars with 9.0 <  K_s, extc <  14.0. In this case, we obtain similar results for stars with 12.5 <  K_s, extc <  14.0. For the three cases, the residuals are similar from θ = 0° to θ = −10°. The blue lines indicate the value of θ that minimizes the residuals.