Hydrogen thermostats at different pressure values. Shown are heat capacities computed for solar elemental composition and pressure values of 1 mbar (typical for the solar temperature minimum region), 0.1 bar (typical for the solar surface), and 5 bar (typical for the TRAPPIST-1 optical surface, see Figure A1). The key message of the figure is that the thermostat temperatures depend on pressure, and therefore vary with the type of star and the height in the stellar atmosphere from which the white-light flare emission originates.