Editing Red-giant branch (section)

===Ascending the red-giant branch===
[[File:Evolutionary track 1m.svg|thumb|Sun-like stars have a degenerate core on the red-giant branch and ascend to the tip before starting core helium fusion with a flash.]]
[[File:Evolutionary track 5m.svg|thumb|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.]]
Stars at the foot of the red-giant branch all have a similar temperature around {{Val|5000|fmt=commas|ul=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 {{solar mass|8}}.<ref name=vandenberg>{{cite journal|bibcode=2006ApJS..162..375V|arxiv=astro-ph/0510784|title=The Victoria-Regina Stellar Models: Evolutionary Tracks and Isochrones for a Wide Range in Mass and Metallicity that Allow for Empirically Constrained Amounts of Convective Core Overshooting|journal=The Astrophysical Journal Supplement Series|volume=162|issue=2|pages=375–387|last1=Vandenberg|first1=Don A.|last2=Bergbusch|first2=Peter A.|last3=Dowler|first3=Patrick D.|year=2006|doi=10.1086/498451|s2cid=1791448}}</ref>

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.<ref name=hekker>{{cite journal|bibcode=2011MNRAS.414.2594H|arxiv=1103.0141|title=Characterization of red giant stars in the public Kepler data|journal=Monthly Notices of the Royal Astronomical Society|volume=414|issue=3|pages=2594|last1=Hekker|first1=S.|last2=Gilliland|first2=R. L.|last3=Elsworth|first3=Y.|last4=Chaplin|first4=W. J.|last5=De Ridder|first5=J.|last6=Stello|first6=D.|last7=Kallinger|first7=T.|last8=Ibrahim|first8=K. A.|last9=Klaus|first9=T. C.|last10=Li|first10=J.|year=2011|doi=10.1111/j.1365-2966.2011.18574.x|doi-access=free |s2cid=118513871}}</ref>

On the ascent of the RGB, there are a number of internal events that produce observable external features. The outer [[Convective zone|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.<ref name=stoesz>{{cite journal|bibcode=2003MNRAS.340..763S|arxiv=astro-ph/0212128|title=Oxygen isotopic ratios in first dredge-up red giant stars and nuclear reaction rate uncertainties revisited|journal=Monthly Notices of the Royal Astronomical Society|volume=340|issue=3|pages=763|last1=Stoesz|first1=Jeffrey A.|last2=Herwig|first2=Falk|year=2003|doi=10.1046/j.1365-8711.2003.06332.x|doi-access=free |s2cid=14107804}}</ref> 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.<ref name=cassisi>{{cite journal|bibcode=2011A&A...527A..59C|arxiv=1012.0419|title=The magnitude difference between the main sequence turn off and the red giant branch bump in Galactic globular clusters|journal=Astronomy & Astrophysics|volume=527|pages=A59|last1=Cassisi|first1=S.|last2=Marín-Franch|first2=A.|last3=Salaris|first3=M.|last4=Aparicio|first4=A.|last5=Monelli|first5=M.|last6=Pietrinferni|first6=A.|year=2011|doi=10.1051/0004-6361/201016066|s2cid=56067351}}</ref>