# Distance of Star Cluster

1. Feb 3, 2010

### ~Sam~

1. The problem statement, all variables and given/known data

An astronomer measures B and V for a large number of stars in a particular star cluster. (All stars in a given star cluster are at essentially the same distance from the Earth.) She then corrects B and V for interstellar absorption, and plots the resulting value of V for each star against its (B-V) colour index.
She then finds a standard CM diagram of MV vs. intrinsic colour index, (B-V)0, that all stars obey (RH and upper scales in Fig. 16.5), and overlays her observed diagram on the standard diagram. Each star's corrected (B-V) equals its intrinsic (B-V)0, so she lines up the plots so the (B-V) and (B-V)0 scales are equal, and then slides the observed diagram vertically to find the best fit with the standard diagram. At the position of best fit, V = 11.0 on the LH scale lines up with MV = 4.4 on the RH scale. What is the distance to the cluster?
(The technique described here is called cluster fitting, and provides an accurate way of finding the distance to a star cluster because it averages out the observational variations in the individual stars.)

2. Relevant equations

3. The attempt at a solution

I'm somewhat lost, I know I need to find the distance, but not sure how. Does it involve distance modulus? m-M=5logD-5?

Last edited: Feb 3, 2010