Absolute Magnitude Calculation, How?

[capcom]

Hello everyone,

Glad to be a new member of this superb forum :)

In one of my physics classes, I have to construct an H-R Diagram. Now, this does not seems too challenging, and I'm sure it isn't.

I was wondering if someone could kindly guide me in the right direction without giving me an exact answer.

So basically, I have been given some info about a star cluster. I have been given measurements taken through blue and yellow filters and told that the top of the main sequence is at B-V = 0.50 and V = 23.48 and bottom at B - V = 2.74 and V = 23.08.

You see, the B and V values are apparent magnitudes. The way I understand HR diagrams, they require absolute magnitudes. I haven't been given any distances to the star cluster, so how can I find an absolute magnitude? The only info I have been given with regards to its location is that it is in the dir'n of a dust cloud in the milky way.

So any recommendations as to how I should approach this. Thanks a lot everyone :)

[Bobbywhy]

capcom, Welcome to Physics Forums!

I used these terms "h-r diagram" to google search and found this worksheet to use for creating the diagram:

http://www.google.com/#hl=en&sugexp=pfwl&cp=14&gs_id=q&xhr=t&q=h-r+diagram+worksheet&pq=h-r+diagram&pf=p&sclient=psy-ab&source=hp&pbx=1&oq=h-r+diagram+wo&aq=0e&aqi=g-e1g1g-v2&aql=&gs_sm=&gs_upl=&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=9fc555e179c890b0&biw=1343&bih=664

Looks like there are a few other options, too. I recommend you check out a few different ones and select the best on for your purpose.

[capcom]

Thanks for your reply!

Actually, it turns out you can use apparent magnitude if the distance of the observed stars is the same.

We can consider the distance to be the same for a star cluster, so there we go - we can use the apparent magnitude.

Thanks again!