How many M type stars equal the luminosity of one O type star?

[blumfeld0]

Hello. what equation do i use to figure out how many .75*Msolar main sequence stars would it take to equal the luminosity of one 3*Msolar O tpe star?
I know O type are much brighter but how many times brighter?

thank you

 

[Labguy]

Hello. what equation do i use to figure out how many .75*Msolar main sequence stars would it take to equal the luminosity of one 3*Msolar O tpe star?
I know O type are much brighter but how many times brighter?

thank you

You ought to be able to get most of this info from links starting on http://www.astronomynotes.com/starprop/chindex.htm" .

or http://www.astro.caltech.edu/~kbundy/ay1page/lectures/class7.pdf".

 

[SpaceTiger]

Hello. what equation do i use to figure out how many .75*Msolar main sequence stars would it take to equal the luminosity of one 3*Msolar O tpe star?
I know O type are much brighter but how many times brighter?

I would use a table, but if you can't find one, the mass-luminosity relation should be fine:

$$\frac{L}{L_{sun}} \propto (\frac{M}{M_{sun}})^{3.5}$$

 

[franznietzsche]

I would use a table, but if you can't find one, the mass-luminosity relation should be fine:

$$\frac{L}{L_{sun}} \propto (\frac{M}{M_{sun}})^{3.5}$$

As a side note this requires that composition (hydrogen, helium, metal mass fractions) be the same. Higher helium content will mean higher luminosity as will lower metal content.