  The motivation to study experimentally CO ice under mimicked interstellar
conditions is supported by the large CO gas abundances and ubiquitous presence
of CO in icy grain mantles. Upon irradiation in its pure ice form, this highly
stable species presents a limited ion and photon-induced chemistry, and an
efficient non-thermal desorption. Using infrared spectroscopy, single laser
interference, and quadrupole mass spectrometry during CO ice deposition, the CO
ice density was estimated as a function of deposition temperature. Only minor
variations in the density were found. The proposed methodology can be used to
obtain the density of other ice components at various deposition temperatures
provided that this value of the density is known for one of these temperatures,
which is typically the temperature corresponding to the crystalline form. The
apparent tendency of the CO ice density to decrease at deposition temperatures
below 14 K is in line with recently published colorimetric measurements. This
work allowed to revisit the value of the infrared band strength needed for
calculation of the CO ice column density in infrared observations, $8.7 \times
10^{-18} ~ {\rm cm ~ molecule}^{-1}$ at 20 K deposition temperature.
