1. The Structural Parameters of the Large Magellanic Cloud
Felicia Werchan Mentor: Dr. Dennis Zaritsky ASGC Statewide Symposium April 18th, 2009

2. The Large Magellanic Cloud (LMC)
Nearby galaxy
About 160,000 light years away
Visible only from the southern hemisphere
Many new stars form inside star clusters
What fraction of stars form in clusters?
Star clusters will often dissolve over time
How fast do they dissolve?
Do all clusters dissolve?

3. The Clusters
LMC 133
LMC 1367
LMC 797

4. Creating the Cluster Catalog
Data for the clusters was taken at Las Campanas Observatory in Chile
Center and brightness profile established for each cluster
Two different models are used to best fit the cluster brightness profiles
King
Has been found to better fit older clusters
Elson, Fall, and Freeman (EFF)
Has been found to better fit younger clusters

5. Creating the Cluster Catalog
King and EFF fits are established using Fortran programming
Both models created files with cluster data
Largest cluster sample analyzed to date
Some clusters were excluded, e.g.,
Cluster close to edge of image
Cluster too diffused to provide usable data
Final cluster catalog: 1066 clusters

6. Fit Parameters Cluster center Background (sky) value
Radius containing 90% of the light: r90
Core radius: rc
Tidal radius: rt
Cluster concentration: log10(rt/rc)

7. King Model log10 (Surface Brightness) [counts arcsec-2]
log10 (Radius) [arcsec]

8. Background Fits log10 (Surface Density) [counts arcsec-2]
Radius [arcsec]

9. King Fit After Background Subtraction
log10 (Surface Density) [counts arcsec-2]
log10 (Radius) [arcsec]

10. Comparison of King and EFF r90
King model associated with higher r90 value in general

11. Comparison of King and EFF χ2
EFF model associated with higher χ2 value
in general

12. Further Research
Characterize relationships of measured parameters to cluster age and mass, e.g.,
Tidal radius
Cluster concentration
Cluster structure (e.g. circular, elliptical, diffuse)

13. Acknowledgements Dr. Dennis Zaritsky
University of Arizona Department of Astronomy
University of Arizona Steward Observatory
Arizona Space Grant Consortium

14. Thank you

15. King and EFF
King
Based from tidally limited models of isothermal spheres
EFF
Accounts for the lack of a developed tidal cutoff