ASTRON 100 Lecture Notes - Binary Star, Planetary Nebula, Thermostat

• School: UMASS-Amherst
• Department: Astronomy
• Course: ASTRON 100
• Professor: Alexandra Pope

Document Summary

Cno cycle (c: carbon, n: nitrogen, o: oxygen) High mass main sequence stars fuse h to he at a higher rate using carbon, nitrogen, and oxygen as catalysts. Greater core temperatures enable hydrogen nuclei to overcome greater repulsion. The initial post-main-sequence stages of high-mass stars are similar to those of low-mass stars: hydrogen core fusion (main-sequence, hydrogen shell burning (supergiant, helium core fusion (supergiant) Big bang made 75% h, 25% he; stars make everything else. Helium fusion can make carbon in low mass stars. Cno cycle can change carbon into nitrogen and oxygen. High core temperature allow helium to fuse with heavier elements. Helium capture builds carbon into oxygen, neon, magnesium, and other elements. Core temperatures in stars with >8msun allow fusion of elements as heavy as iron. Advanced reactions in stars make elements like si, s, ca, and fe. Advanced nuclear burning proceeds in a series of nested shells.