# Luminosity of M type/Otpe

1. Jul 17, 2006

### 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

2. Jul 17, 2006

### Labguy

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

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

Last edited by a moderator: May 2, 2017
3. Jul 17, 2006

### SpaceTiger

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

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

4. Jul 17, 2006

### franznietzsche

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.