Stars in Group 2, represented in red on the HR Plot, are in the Red Giant stage, characterized by higher luminosity and lower temperature compared to their main sequence counterparts.
Stars in Group 2, depicted in red on the Hertzsprung-Russell (HR) Plot, signify that they are in the Red Giant stage of their life cycle. The positioning of stars in this group on the HR Plot provides valuable information about their temperature and luminosity characteristics during this particular stage. Red Giants have higher luminosity, indicating increased brightness, compared to when they were in the main sequence phase.
Simultaneously, their temperature is lower during the Red Giant stage, resulting in their placement in the upper-right region of the HR Plot. This shift in position reflects the expansion of the outer layers of these stars as they exhaust their hydrogen fuel in the core, causing them to become larger, cooler, and more luminous. The HR Plot thus serves as a visual representation of the evolutionary progression of stars, allowing astronomers to discern key features of different stellar life stages.