Illustration showing the stable layer boundaries in (x, T) space. Solid curves use data (Seward & Franck 1981, see Sect. 2.3), while dashed curves use the ideal gas approximation x = p_s/p, diverging near the critical endpoint. Gray shaded areas are regions of parameter space wherein free convection is permitted. In the top-right corner, the gray region lies beyond the critical curve where phase separation does not occur. At the bottom of the figure, the gray region lies below the x_inh curve described in Eq. (2). Blue, magenta, and red curves represent hydrostatic pressure environments of 300 bars, 1 and 2.5 kbars respectively. The solid points where the dashed curves intersect correspond to the top of the stable layer under the ideal gas approximation; the red asterisk shows the offset intersection using data. The open circles where the solid colored curves intersect the critical curve represent the top of the core.