P07: Globular Cluster Radii
Observing Goals:
In this project you will determine the surface brightness profile and a characteristic scale of a globular cluster (or clusters if there is sufficient observing time). Useful Background and References:
Information about King models http://adsabs.harvard.edu/abs/1995AJ….109..218T
Core radii of globular clusters http://adsabs.harvard.edu/abs/1995AJ….109..218T
Observation Planning:
Observation Time
You will be observing HALF a night.
Target Selection
It is best to find a Messier object that is a Globular Cluster (something with an M-number) as those will likely be large and bright enough. Make sure your choice will be high in the sky during your obsering time.
Observations
Take images in the B and R bands at least, and also the V band if you have time.
Observe standard star fields so that you will be able to calibrate your results.
Data Analysis:
Data Reduction Basic Steps
Visit the page Data Reduction Cheat Sheet
Register and combine your images so that you have one final image in each band.
Further for this project
Measure the sky brightness level in the images (e.g. in the corners) and remove this from the whole image.
Locate the center of the globular cluster in the image; here a contour plot can be very useful!
Next, measure the surface brightnes profile by fitting elipses moving outwards from the center (note there are astropy routines that help with this)
Further Analysis for this project
You can now plot your surface brightness profile and fit a King model. Find the value of the core radius from your fit and compare that to published results.
Results:
Can you answer these questions with your work?
What is the surface brightness profile of your globlar cluster (or clusters)?
What are the King model fit parameters for your cluster (or clusters)?
How does your measured core radius compare with published results?