page_title: Red-giant branch
section_title: Ascending the red-giant branch
hierarchical_section_title: Red-giant branch / Evolution / Ascending the red-giant branch
context_page_description: The red-giant branch, sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass stars. Red-giant-branch stars have an inert helium core surrounded by a shell of hydrogen fusing via the CNO cycle. They are K- and M-class stars much larger and more luminous than main-sequence stars of the same temperature.
context_section_description: Stars at the foot of the red-giant branch all have a similar temperature around 5,000 K, corresponding to an early to mid K spectral type.  Their luminosities range from a few times the luminosity of the sun for the least massive red giants to several thousand times as luminous for stars around 8 M☉.
  As their hydrogen shells continue to produce more helium, the cores of RGB stars increase in mass and temperature.  This causes the hydrogen shell to fuse more rapidly.  Stars become more luminous, larger, and somewhat cooler.  They are described as ascending the RGB.
  On the ascent of the RGB, there are a number of internal events that produce observable external features.  The outer convective envelope becomes deeper and deeper as the star grows and shell energy production increases.  Eventually it reaches deep enough to bring fusion products to the surface from the formerly convective core, known as the first dredge-up.  This changes the surface abundance of helium, carbon, nitrogen, and oxygen.  A noticeable clustering of stars at one point on the RGB can be detected and is known as the RGB bump.  It is caused by a discontinuity in hydrogen abundance left behind by the deep convection.  Shell energy production temporarily decreases at this discontinuity, effective stalling the ascent of the RGB and causing an excess of stars at that point.
caption: Stars more massive than the sun do not have a degenerate core and leave the red giant branch before the tip when their core helium ignites without a flash.