Assume a galaxy forms its stars in a single rapid burst, with a Salpeter initial mass...

Assume a galaxy forms its stars in a single rapid burst, with a Salpeter initial mass function extending from 0.1 to 100 Msun. After 10 Gyrs have passed, divide the surviving stars into three groups: lower main-sequence upper main sequence (MS stars with mass > 0.75 Msun), lower main sequence (MS stars with mass < 0.75 Msun), and red giants. Calculate the fractional contribution of each group to:  

(a) the total number of surviving stars. (b) the total mass in surviving stars. (c) the total luminosity of the galaxy.

Hints: Assume the MS lifetime-vs-mass relation and RGB lifetimes as given in Lecture I. Ignore post-RGB evolutionary stages. For MS stars, assume luminosity-mass relation of (L/Lsun) = (M/Msun)3.5. Assume (crudely) that the average RGB luminosity is ~100 times higher than the turn-off luminosity.  

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genius_generous answered 1 year ago

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