Left panel. Dependence of the redshifted surface temperature (logarithmic scale) on time for the values of the transition temperature T^∗ (in MeV) indicated in the plot and for fixed width w = 0.2 MeV. We also show the same dependence for T^∗ = 0.093 and w = 0.3 (dash-double-dotted line) and w = 0.1 (double-dash-dotted line). The underlying model is the 1.93 M_⊙ compact star model of Knippel & Sedrakian (2009). Right panel. Dependence of the redshifted surface temperature (in units of 10⁶ K) on time for the same model. The points with error bars show the Cas A data, and the solid lines are fits to these data by variation of T^∗ for fixed width w = 0.2 MeV. The redshifted temperature measured by a distant observer is obtained as , where φ_S is the surface value of the function φ, which is defined via the temporal component of the spherically symmetrical metric according to g₀₀ = e^2φ.