  The modification of the ground state properties of light atomic nuclei in the
nuclear and stellar medium is addressed, using chemical equilibrium constants
evaluated from a new analysis of the intermediate energy heavy-ion (Xe$+$Sn)
collision data measured by the INDRA collaboration. Three different reactions
are considered, mainly differing by the isotopic content of the emission
source. The thermodynamic conditions of the data samples are extracted from the
measured multiplicities allowing for a parametrization of the in-medium
modification, determined with the single hypothesis that the different nuclear
species in a given sample correspond to a unique common value for the density
of the expanding source. We show that this correction, which was not considered
in previous analyses of chemical constants from heavy ion collisions, is
necessary, since the observables of the analyzed systems show strong deviations
from the expected results for an ideal gas of free clusters. This data set is
further compared to a relativistic mean-field model, and seen to be reasonably
compatible with a universal correction of the attractive $\sigma$-meson
coupling.
