ASTR 1346 1st Edition Lecture 12 Outline of Last Lecture I Hydrostatic Equilibrium II Evolutionary Events for Stars Outline of Current Lecture I Mass Ranges A Low Mass Stars II Core Contraction III Electron Degeneracy IV Helium Flares and Carbon Core V Planetary Nebula Stage Current Lecture l Less than 08 solar mass failed stars 08 4 solar mass extremely low mass star 4 8 low mass star 8 25 intermediate mass star 25 high mass star A Our Sun is a low mass star In low mass stars Helium is convected upward and hydrogen downward The entire star becomes a Helium star This takes 100 s of billions of years and no stars have done this yet because our galaxy is too young These stars have a helium core hydrogen burning shell and non burning envelope Core is contracting and temperature increases turning helium into hydrogen which expands and pushes radiation pressure outward Temperature of the Sun decreases overall and as it gets bigger it gets brighter ll As core contraction continues the amount of inert helium increases shell burning adds more helium ash There is no energy generated in the core and the gravity contracts the core Temperature in core increases reaching 100 million K lll These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Before Helium burning starts core density is very high At this density electrons become degenerate Degeneracy pressure is independent of temperature lV Helium burns rapidly for a few hours helium flares then slows down to normal rate Helium starts burning in the core to form carbon with normal rate then it will be all carbon in core Nuclear fusion will stop when this happens and the core will be overpowered by gravity and start contracting again and temperature will rise again V The planetary nebula stage is when slowly the stellar envelope separates from the core and goes back out to space leaving a hot core with low luminosity white dwarf The core then stays there for a long time cooling off