dwarfs (later than T7 dwarfs and possible Y dwarfs) candidates. The rationale of the NIR follow-up is the following.

-   A short (5 to 10 minute dithered image, with 30-s individual exposures), $J$-band exposure confirms the candidate and eliminates any remaining contaminants from variable sources, such as supernovae or detector artefacts. For confirmed candidates, this image also provides good signal-to-noise (from 20 to about 100, depending on the target magnitude) $J$-band photometry, better than the photometry on the detection image.

-   All candidates confirmed with this SOFI $J$ photometry are imaged in $H$-band to characterise them as ultracool brown dwarfs or earlier T-dwarfs. A 10-20 minute dithered sequence, with 20-s individual exposures, usually achieve good signal-to-noise photometry, with an accuracy better than 5%.

-   All confirmed candidates with measured $J-H<$0.1 are potential ultra-cool brown dwarfs that can be further characterised by acquiring $K_{\rm s}$-band photometry, if enough observing time is available. A 15-30 minute dithered sequence, with 15-s exposures typically achieves good signal-to-noise photometry in $K_{\rm s}$.

It should be noted that this very efficient confirmation and characterisation photometric follow-up is made possible by visitor-mode observation combined with the automatic image reduction by SOFI pipeline *Gasgano*. A simple photometric analysis 