The stellar limb of a red giant is not sharply defined, contrary to their depiction in many illustrations. The second, and sometimes third, dredge up occurs during helium shell burning on the asymptotic-giant branch and convects carbon to the surface in sufficiently massive stars. The first dredge-up occurs during hydrogen shell burning on the red-giant branch, but does not produce a large carbon abundance at the surface. Asymptotic-giant-branch stars range from similar luminosities as the brighter stars of the red-giant branch, up to several times more luminous at the end of the thermal pulsing phase.Īmong the asymptotic-giant-branch stars belong the carbon stars of type C-N and late C-R, produced when carbon and other elements are convected to the surface in what is called a dredge-up. Stars on the horizontal branch are hotter, with only a small range of luminosities around 75 L ☉. Red-giant-branch stars have luminosities up to nearly three thousand times that of the Sun ( L ☉), spectral types of K or M, have surface temperatures of 3,000–4,000 K, and radii up to about 200 times the Sun ( R ☉). Despite the lower energy density of their envelope, red giants are many times more luminous than the Sun because of their great size. However, their outer envelope is lower in temperature, giving them a yellowish-orange hue. They have radii tens to hundreds of times larger than that of the Sun. The K0 RGB star Arcturus is 36 light-years away, and Gamma Crucis is the nearest M-class giant at 88 light-years' distance.Ī red giant will usually produce a planetary nebula and become a white dwarf at the end of its life.Īn illustration of the structure of the Sun and its possible future as a red giant, comparing their structure and size.Ī red giant is a star that has exhausted the supply of hydrogen in its core and has begun thermonuclear fusion of hydrogen in a shell surrounding the core. Many of the well-known bright stars are red giants because they are luminous and moderately common. asymptotic-giant-branch (AGB) stars with a helium burning shell outside a degenerate carbon–oxygen core, and a hydrogen-burning shell just beyond that.
red-clump stars in the cool half of the horizontal branch, fusing helium into carbon in their cores via the triple-alpha process.most common red giants are stars on the red-giant branch (RGB) that are still fusing hydrogen into helium in a shell surrounding an inert helium core.Red giants vary in the way by which they generate energy: The appearance of the red giant is from yellow-white to reddish-orange, including the spectral types K and M, sometimes G, but also class S stars and most carbon stars. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around 5,000 K (4,700 ☌ 8,500 ☏) or lower. A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ( M ☉)) in a late phase of stellar evolution.
0 kommentar(er)
