For these stars, the hotter they are, the brighter. These stars have depleted their hydrogen supply and are very old. The core contracts as the outer layers expand. These hot, shrinking stars have depleted their nuclear fuels and will eventually become cold, dark, black dwarfs. Strong UV continuum.
Metallic lines become noticeable.
Sun , Capella K Orange to Red 3,500 - 5,000 K 0.8 0.9 0.4 Metallic lines, some blue continuum. Some molecular bands of titanium oxide. In the Yerkes classification scheme, stars are assigned to groups according to the width of their spectral lines. These stars' energy comes from nuclear fusion , as they convert Hydrogen to Helium. For these stars, the hotter they are, the brighter they are.