This diagram shows the relationship between surface temperature and absolute brightness of a star.
Every hotly (= massive) is a star, the more luminous it is also. Similar to the HRD / FHD also the main sequence and the branch of the giant star is clearly visible.
<br>
In the database are also a couple of young white dwarfs, which are not very cool. This can be seen in the diagram to its high temperature (> 25 000 Kelvin) and the lower luminance (smaller than that of the giant stars).