tokens: to the study would be to ensure that observations of a given object on all telescope configurations are all carried out well within the expected Keplerian orbital time at the inner rim. This would allow a possible smoothing out of the asymmetric emission to be lifted. A second improvement would be to push for a higher angular resolution at VLTI using the longest baseline (≈ 200 m). This implementation is currently under study at the European Southern Observatory (ESO). Finally we note that some objects are sufficiently to the north so that they could be observed with VLTI and the Center for High Angular Resolution Astronomy (CHARA), which would provide a remarkable ( u , v ) coverage and angular resolution. Table 5 Sizes of the stellar environments: theoretical sublimation radius ( θ sub ) and the measured half-flux radius ( θ 1∕2 ). 5.5 Comparing the images to the theoretical dust sublimation radius We can measure the sizes of circumstellar emission from the images by taking the half-light radius corrected for the disk orientation (see Appendix D ). We assessed the accuracy of the size measurement against the true sizes from radiative transfer models in Appendix F by reconstructing images on the synthetic data generated from those models. The recovered sizes match the true sizes of the models with a sharp inner rim as long as the inner rim is resolved enough (i.e., θ 1∕2 ∕ θ res ≥ 1.2). However, we find a bias for sizes from extended inner rim models (see Appendix F ). We tend to recover sizes that are smaller than the true sizes for very resolved targets (i.e., θ 1∕2 ∕ θ res ≥ 2.5). Most of the targets (12/15) are relatively well resolved (i.e., θ 1∕2 ∕ θ res ≥ 1.3). In Fig. 8 , we plotted the sizes of the targets against their luminosity for both this work and L17. For the imaged object, we see good agreement between both size determinations, that is, using parametric models and image reconstruction. For some targets (HD 145718 and R CrA), the difference is significant (ratio larger than 1.5 between the two sizes) and this is likely due to model bias (as the parameteric model for R CrA was an ellipsoid instead of a ring and the stellar-to-total flux ratios are different for HD 145718). We note that the size difference is in the opposite direction of the size bias from image reconstruction that we identified in Appendix F . Fig. 8 Size-luminosity relation. The green circles are the sizes measured from images, red crosses are the sizes from parametric models as determined in L17, and cyan triangles are the physical spatial resolution reached by our observations. The two size estimations and the spatial resolution are linked by a vertical dotted line. The dashed gray line represents the theoretical sublimation radius. In order to have a reference to interpret the sizes of the circumstellar emission from the reconstructed images, we computed the theoretical dust sublimation radii using: (see, e.g., Monnier Millan-Gabet 2002 ; Kama et al.
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