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Lecture

Astronomy - Session 10

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Department
Astronomy
Course
ASTA02H3
Professor
Parandis Khavari
Semester
Winter

Description
 Astronomy – Session 10  mass-age  main sequence stars  near the end of the lives of main sequence stars  become red or yellow giants  main sequence stars    (I): intensity   mass  consumption rate   table 7.2  O stars are young  M stars are old  age is approx.  universe  age is approx.  M stars are older than the universe  how  main sequence  protostars  currently no red dwarfs in their final stages  none are near death  approx.  90% of lifespan spent in the main sequence stage  10% of lifespan spent in stages other than the main sequence stage  Q. Star A is five times that of star B: What can be deduced about their luminosity and lifetimes? *Make use of the constant of proportionality for (such) comparison questions.  (II)    note:   What can be said about the age?   note: the second last ‘equal’ sign is similar to:  note: recall that   one source of energy for main sequence stars  burning of Hydrogen Helium  CNO cycle  p-p chain  Hydrogen in the core being depleted  one change from pressure    number density  Boltzmann constant  temperature   decrease in pressure leads to a decrease in number density ( )  as main sequence stars grow older  grow to be larger in diameter  become colder  if protostars are lower than  cannot start producing Helium  Q. Why does luminosity vary so much?   note: radius is to the power of two  and   radius ranges from  mass ranges from   Vogt-Russell Theorem (not in the textbook)  entire evolution of a single star (not in a binary system)  determined by its mass and its chemical composition   only Hydrogen and Helium (were formed) from the big bang  traces of Carbon and etc. in new generations of stars  the more massive a star, the faster it dies  determines how it dies  law of energy transport  requires hot regions to transfer energy to cold regions  three methods  1. conduction  2. convection
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