working out the distances of galaxies using O type stars.

[Galactic Wanderer]

again been looking around the internet for this one have no idea how to answer it.

 

O type stars in a faint galaxy are observed to be magntiude 15. Estimate the distance to this galaxy.

 

seb xx

[JamesF]

Can type O stars be used as a standard candle?  I wasn't aware that they could, but what do I know?

James

[PhotoGav]

M = m + 5 - 5*logd (where d is in parsecs)

Read off M from the Hertzsprung-Russell diagram for an O class star

m = 15

Plug the numbers in, rearrange for d = and hey presto, you have a distance...

[coatesg]

This sounds like a homework question...

As above, there's not really enough information to solve accurately as O type main sequence stars have a range of absolute magnitudes (range ~ 2 mags).

Photogav's answer is the way you'd do it though, for this type of question, at least for non-cosmological distances.

[PhotoGav]

If you use -5 as the Abs Mag for an O type star, the answer is rather neat!