Ast 105 1nd Edition Lecture 12 Outline of Last Lecture (#12)I. Giantsa. 6 steps to form II. Helium Fusiona. Helium flashIII. Variable Starsa. Instability strip b. Low-mass starsc. High-mass starsd. Ceiphadse.Outline of Current Lecture (#13)I. Death of starsII. AGB starsIII. White DwarfIV. Electron Degeneracy PressureV. Chandra Sakhar VI. NovaVII. Roche LimitVIII. Low and High Mass stars Current LectureDeath of Stars- Is dependent on the main sequence mass- low mass stars < 8 Msun Low Mass Stars- The max temperature is only 200 million Kelvin, therefore no fusion of carbon or oxygen- As the helium fusion in the court begins to slow down, photon production drops off Gravity begins to dominate and enter regions again contract This heats up the shell of helium just above the core, thus shellhelium fusion begins- Just above this we have hydrogen shell fusion- The helium fusion in the shell pushes the outer regions of the star to larger radii, this forms an aymptonic giant branch star (AGB Star)- At the end of AGB, Helium shell flashes occur (more than once) This causes the outer layers to expand and thus cool, and the electrons combined with ions to form atoms  this produces more photons Helium shell flashes and recombination photons a large production of protons- thus (outermost regions) materials ejected is called “planetary nebula”- As the outer regions are blessed away, the hot interior region of the star is exposed the star moves leftward on the H2 diagram (inner regions are at a much higher temp.White Dwarf- As outer layers of both the way, the high temp carbon oxygen core is exposed.This forms a white dwarf- White dwarfs are stable.  The gravity is balanced by electron degeneracy pressureElectron Degeneracy Pressure - The carbon and oxygen are ionized.  Electrons are separated from the nuclei- Nuclei are squeezed into a crystalline arrangement- Electrons distributed around crystals, but are very close to each other- Electrons do not like to be next to each other Pauli Exclusion Principle- As gravity tries to force electrons together, many of them vibrate faster and faster so that the quantum numbers are not identical  This vibration of electrons pushes against the contraction forces of gravityChandraSekhar - In 1940, he found that as long as the mass of the white dwarf was less then 1.4 Msun, the electron degernacy pressuer could balance gravity - limit: white dwarf masses are less than 1.4Msun - Our son will end up as a white board. - 1 teaspoon of white dwarf ways five timesNova In binary systems with a main sequence and white wharf, main sequence Is within the Roche limit of the white wharf, the hydrogen is pulled off the main sequence and onto the white dwarfhydrogen fusion explosion Nova Roche Limit Gravity of a white dwarf is greater than the self-gravity of main sequenceHigh Mass Star- >8 Msun- Here, gravity is sufficient to collapse the core after hearing infusion and drivethe temperature to over 600 million K- For the larger stars, temps get even higher.  This is how almost all of the elements are made- The large number of fusion generated photons created in shells pushes the outer layers far awaythis forms a