Here's a magnitude problem that involves a few of the steps we discussed in class. Please submit the answer by next Tue, Nov 4. Be sure to follow (and show) the method we discussed:

• Outline what you know and the steps you need to take
• Do ball park estimates where appropriate
• show step by step calculations - show all your work

The integrated V magnitude of the 100 billion stars in the Andromeda galaxy is 3.4. Its nucleus of about 20 billion stars can just be seen with the naked eye, that is, it has an integrated magnitude of about 4. The other 80 billion stars reside in the disk of the galaxy. About 25% of them are bright young stars while the rest are fainter old stars only 10% as bright as the young bright disk stars.

1. What is the magnitude of a single average OLD star in the disk?
2. Pretend that the galaxy is face on and that the nucleus is 0.5 degrees in diameter and the whole galaxy is 3 degrees in diameter. If an exposure is taken such that the average pixel count of the disk is 1000, what will be the average pixel count of the nucleus?

This section added to assignment (Oct 30^th, 2003):

Lets say that the nucleus stars have a B-V of +1

• In Disk, Bright stars have B-V = 0
• In Disk, Faint stars have B-V = 2

Recall that the Andromeda Galaxy has a V=3.4

3. What is the B-V of the Andromeda Galaxy given the above assumptions?
4. What is the absolute magnitude of a single faint disk star in the Andromeda galaxy?

No one step is very complex so take your time and figure out how to break it down into a series of simple steps.

Let me know if you have any questions,
Chris