Location of S CrA N in the size-luminosity diagram: K-band ring-fit radii derived with a geometric ring-star model (pink square,  ≈ 0.13 AU) and a ring-star-halo model (blue square,  ≈ 0.11 AU); see Tables 3 and 1 for the stellar parameters used. The lines indicate the predicted theoretical dependence of the K-band radius on the luminosity (Monnier & Millan-Gabet 2002). Predictions of models including backwarming are discussed in Sect. 4. The filled black squares are a sample of Herbig Ae stars (Monnier et al. 2005). The open black squares represent a sample of TTS (Pinte et al. 2008).