"I will describe two dedicated campaigns with the VST, which exploit its fast optics and high image quality, and will extend its survey capabilities in the spectroscopic and time-domain.
The first project consists in high-cadence monitoring of strongly lensed quasars, for time-delay cosmography. With the eCOSMOGRAIL collaboration, we are performing (almost) nightly-cadence campaigns on bright Southern lenses, aiming at 2% accuracy and precision on H0, and the VST will be the ideal telescope to extend these on a larger sample of lenses discovered before 2020, reaching sub-percent uncertainties on H0. By comparison, the three-night (foreseen) cadence of LSST is sufficient only for lenses with long delays.
The second project is a slitless-spectroscopic survey, which will provide accurate redshifts for the LSST-Euclid synergy, an accurate and wide-field object classification, and the discovery of intrinsically rare objects. Being optically ""fast"", the VST can survey very wide footprints to a target depth of i=21, and its excellent image quality guarantees an accurate separation of overlapping spectra. Medium-low resolution spectroscopy will yield an unbiased coverage of emission-line objects (e.g. quasars up to z=4), a large sample of extremely metal poor stars, and the external calibration needed in the LSST-Euclid synergy to break degeneracies (between E(B-V), spectral type, and redshift) in photo-z determination, beyond the forecasted ~0.01 accuracy limit from broad-band information only."