Example of masks used for aperture photometry measurements: the ±45° sector (right panel) and the annulus (left panel) superimposed on a VIRTIS-M image at 1100 nm (selected to show the nucleus at the same scale). The two vertical axes in each image show the operation mode of VIRTIS-M: the instrument scans spatially (number of the line on the left) and temporally (time on the right) through the coma and nucleus of the comet. The green line indicates the mid-point inside each mask for the ±45° sector and the full annulus.