A very strange curve on P-V diagram

[mech-eng]

Hi. For a state of nitrogen in which temperature is higher than the critical temperature the state is presented on a different curve. I do not remember any curve for superheated region.

Source: Introduction to Engineering Thermodynamics by Sonntag/Borgnakke.
Thank you.

 

[Chestermiller]

Hi. For a state of nitrogen in which temperature is higher than the critical temperature the state is presented on a different curve. I do not remember any curve for superheated region.

View attachment 197173

Source: Introduction to Engineering Thermodynamics by Sonntag/Borgnakke.
Thank you.

Is there a question here?

 

[mech-eng]

Is there a question here?

Yes, what is that curve which point a stands on?
Thank you.

 

[Chestermiller]

Yes, what is that curve which point a stands on?
Thank you.

It's an isotherm, for a temperature above the critical temperature.