Top: VLTI/GRAVITY interferometric data (colored) and best fit binary model (solid black) for Delta Capricorni. The dashed lines show the corresponding model for the resolved primary alone. Bottom left: differential visibility phases (colored) across the Brγ absorption line of the primary star showing the typical S-shaped signature of spatially resolved rotation. Bottom right: centroid position of each wavelength channel across the Brγ line relative to the continuum. The resulting projection of the primary’s rotational plane (Ω_rot) is shown in magenta lines (3σ errors in dashed lines) compared to the line of nodes of the orbital plane (Ω_orb).