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AST 443
Ch - 20
Problems
5. The Sun will reside on the main sequence for 1010 years. If the luminosity of
a main-sequence star is proportional to the fourth power of the star’s mass,
what mass star is just now leaving the main sequence in a cluster that formed
(a)
400
million
years
ago,
(b)
2
billion
years
ago?
8. Calculate the average density of a red-giant core of 0.25 solar-mass and
radius 15,000 km. Compare this with the average density of the giant’s
envelope, if it has a 0.5 solar-mass and its radius is 0.5 A.U. Compare each
with the central density of the Sun.
9. A 15-solar-mass blue supergiant with a surface temperature of
20,000 K becomes a red supergiant with the same total
luminosity and a temperature of 4000 K. By what factor does its
radius change?