Comparison between the observed interferometric data (data set #3) and the MARCS model. In all panels, the black thin lines represent the predictions of the MARCS model with the parameters most appropriate for BK Vir (see Sect. 4.2). The thick colored lines represent the observed data. a) Spectrum. Residuals of the strong telluric lines are marked by  ⊕ . b) − d) Visibilities on the 15.9, 31.8, and 47.8 m baselines, respectively. e) Closure phase.