WeMedipati, C.Chandrasekaran, N.Falsett, C.Colonna, P. experimentally investigate the nature of propagation of rarefaction waves in the dense vapors of the organic fluid dodecamethylcyclohexasiloxane, D \(_6\) . The experiments were performed in the Asymmetric Shock Tube for Experiments on Rarefaction Waves (ASTER) facility that is designed to withstand pressures and temperatures of up to 15 bar and 400  \(^\circ \) C, respectively. Recent improvements to the test facility allow the accurate control of fluid temperature and pressure during heating, cooling, and the expansion process. To ensure temperature homogeneity of the working fluid during the isochoric heating process, temperature measurements were performed simultaneously at various locations in the axial direction of the shock tube and under different heating conditions. The propagation velocity of the rarefaction waves was measured at various thermodynamic states of the fluid by employing the time of flight method. The deviation of the fluid behavior from classical gasdynamic behaviour was observed with repeatability when the thermodynamic state of the fluid was close to its thermal stability limit.