The grade of each observing block (OB) is set by the on-site VLT observer based on the user-requested ambient conditions (seeing, sky transparency, airmass) vs. the actual observing conditions. A grade “A” means that the conditions were fully within specifications, “B” that they were mostly within specifications, while “C” means they were out of specifications and the OB should be repeated if possible;

on source = DIT  ×  NDIT  ×  number of OBJECT frames;

average astronomical site monitor seeing at start in the visible (0.5 μm) and at the zenith (airmass = 1). This value can differ significantly from the NACO image quality, which is usually better. “NA” means that no seeing data was available for this night;

average coherence time of the atmosphere at 0.5 μm calculated by the real time computer (RTC) on real data. Short values of τ₀ (<6 ms) represent a seeing not stable in time;

computed with eclipse in the final processed image;

of the star in the processed image adopting a Moffat fitting to the radial profile. The full width at half-maximum (FWHM) of the diffraction-limited PSF for the VLT at 2.12 μm is 65 mas;

optical magnitude retrieved from SIMBAD: 1) DoAr 21 – Cieza et al. (2007), 2) HD 135344B – Høg et al. (2000), 3) HR 4796A – Barrado Y Navascués (2006); 4) T Cha – Tanner et al. (2007); 5) TW Hya – Torres et al. (2006);

DoAr 21: PSF saturated in the central pixels (4 to 7 pixel range); T Cha: elliptical along x-axis; PSF calibrators HD 144156 and HD 94889 have close companions at d = 133, PA = 20° and d = 22, PA = 260°, respectively.