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# ASTA02H3 Lecture Notes - Main Sequence, Number Density, Boltzmann Constant

Department
Astronomy
Course Code
ASTA02H3
Professor
Parandis Khavari

Page:
of 7
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