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Reference.org
Red-giant branch
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<p>The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of <a href="/facts/Stellar_evolution/Qa4vAGmn">stellar evolution</a>. It is a stage that follows the <a href="/facts/Main_sequence/DJ3Wq8kd">main sequence</a> for low- to intermediate-mass stars. Red-giant-branch stars have an inert <a href="/facts/Helium/yRul93TG">helium</a> core surrounded by a shell of <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a> fusing via the <a href="/facts/CNO_cycle/ClM5eAGc">CNO cycle</a>. They are K- and M-class much larger and more luminous than main-sequence stars of the same temperature. </p>