I spent 4 nights observing at the CTIO .9-m telescope.
The site, El Cerro Tololo is next to Cerro Pachon, where the LSST auxiliary telescope will be built.
Besides the usual calibrations frame (bias dark and domeflats), I dedicated the observations to an extensive follow up of two Calspec stars, HD14943 and MuCol, so as to get a fine timeline monitoring of the relative variation of the atmospheric transmission.
The ~700 images will now be reduced to extract the spectra and measure the relative variation of atmospheric absorption as a function of airmass for 4 nights.