Project #8 The Color of Galaxy
[Draft]
The purpose of this exercise is to see if the color of a galaxy is uniform over its surface.
You cannot get credit for this lab and 'the Hunt for Galaxies' lab,
Preparation
The goal is to measure the color difference (if any) in different parts of a galaxy outside the Milky Way. You need to pick a galaxy that is bright enough to give good data. There are several bright galaxies at http://www.seds.org/messier/objects.html#galaxy. It is going to be hard to find most galaxies but you can try one from the hunt for galaxies lab. You best choice of nights will be when there is no moon. You might also go to http://skyview.gsfc.nasa.gov/ to get a picture of the galaxy and the stars around it. It is likely that the entire galaxy will not fit onto the CCD. If it doesn’t, plan how you are going to place the exposure to measure the entire width of the galaxyObservations
You want to take good exposures from the center of the galaxy outward until
the edge. You need exposures in V and I.
Make sure the galaxy is exposed long enough to show up over the background. You may need to take pictures of the
galaxy piece at a time. If you do,
overlap the pictures a bit. As you
move to fainter parts of the galaxy you need to increase the exposure times.
Reduction and analysis
Pick a standard aperture area and measure different sections of the galaxy
starting from the middle. Count
the center as 0,0 and record both position and intensity of each measure. Measure the same aperture area well
away from the galaxy on the same frame.
Use this as the background and subtract it from the light of the galaxy. Plot the brightness vs. distance from
the center of the galaxy for each color.
Then divide the measures V/I and plot that vs. distance from the center. How does the color change as you go from
the center to the edge of the galaxy?
Write-up
If you took more than on CCD image of different sections of the galaxy show the positions of the pictures on the Skyview plot. Show and explain your plots.