L\AMP M bands medium resolution (R ∼ 500) observation of the Be binary δ Cen obtained in GRA4MAT mode. From top to bottom: source spectrum, cleaned 10 s frame (i.e. with the mean sky removed) in the interferometric channel, differential squared visibility for one of the six baselines, and corresponding differential phase. The gap between the L and M band is shown in grey in the visibility and phase plots. The source spectrum shows a rich collection of hydrogen emission lines in Brα and the Humphrey and Pfund series. The interferometric channel of MATISSE composed of straight and stable high contrast fringes from 2.9 to 4.9 μm shows a collection of bright source emission lines and dark telluric absorption lines.