(a) Averaged IR excess of ℓ Car as derived with the SPIPS algorithm (red dots) and presented with the fitted ad hoc analytic law . For each photometric band (described in Appendix A), the red dots are the mean excess value averaged over the cycle of pulsation of ℓ Car while the blue uncertainties correspond to the respective standard deviation. (b) The IR excess of ℓ Car is reconstructed at the specific phase of Spitzer observation. It includes the averaged IR excess from SPIPS (red dots) and the Spitzer observations (blue line) corrected for the silicate absorption of the ISM along the line of sight (orange curve). The silicate extinction was derived using silicate refractive index from Draine & Lee (1984). Green and gray vertical stripes represent the LM and N bands of MATISSE, respectively.