Visibility amplitudes as a function of baseline length, shown for the continuum (averaged for 4.04-4.05 μm and 4.054-4.06 μm; blue), and at the peak of the Brα line emission at 4.052 μm (red). The observed visibilities are fit to three different brightness distributions: a Gaussian (top), a uniform disc (middle), and a ring (bottom). By fitting these models to the observed visibilities, we infer the characteristic size of the emitting region for both the continuum and the Brα emission. The fitted size and reduced χ² values for each model are indicated in the corresponding panels, allowing comparison of model performance.