The HR diagram contains only stars - so everywhere.
Of course they are on the HR diagram. They are simply not on the main sequence.
All stars.
main-sequence stars
The main reason that the HR Diagram is so useful and important to scientists is, you can tell the size of the star by plotting it on the HR Diagram. The different sizes of stars form a pattern on the HR diagram.
stars there called stars
stars there called stars
The red dwarves.
Main sequence
They are very hot stars.
The HR diagram does not reference stars on their way to the main sequence, only during or after.
The curve that currently contains most stars on the HR diagram is called the "main sequence". It consists of those stars that fuse hydrogen-1, converting it into helium-4.
Yes.