Comparison between the observed o Aquarii and model SEDs from the ultraviolet to the far-infrared region. Flux unit is in erg cm⁻² s⁻¹ Å⁻¹ and wavelength is shown in logarithmic scale. IUE/SWP and IUE/LWP spectra are shown in black line and photometric data in black points. Top panel: purely photospheric models (color lines) with variation in the stellar radius (no inclusion of geometrical oblateness): R_⋆ = 3.2 R_⊙ (orchid), 4.0 R_⊙ (red), and 4.4 R_⊙ (green). Bottom panel: photospheric model with 4.0 R_⊙ (red) and our best-fit HDUST model from fitting all the interferometric data (dashed blue line; Table 5). Note that the UBV-bands are better reproduced with R_⋆ = 4.0–4.4 R_⊙. Our best HDUST model reproduces the observed IR excess due to the circumstellar disk well.