A study of the ages of Large Magellanic Cloud star clusters

1. A study of the ages of Large Magellanic Cloud star clusters Randa Asa’d University of Cincinnati Adviser: Dr. Margaret Hanson Bucuresti 23 Septembrie 2010 asadrs@mail.uc.edu

2. Introduction • Studying the physics of star clusters helps us understand the evolution and structure of galaxies. • The Large Magellanic Cloud (LMC) galaxy is a good object to develop a new, revised calibration system between CMD and photometric ages. The LMC is a nearby galaxy at a distance of 160,000 light years. • As a star grows older, it will eventually exhaust all of its • hydrogen fuel, resulting in a dramatic expansion in size • coupled with an increase in luminosity to become a • red giant, the star leaves the main sequence and moves • towards the upper right corner of the CMD. • (We compiled a list of 86 clusters with ages and integrated colors) asadrs@mail.uc.edu

3. Photometric age Hunter Catalog: (Hunter et al. 2003) compares the data with the Starburst99 (Leitherer et al. 1999) evolutionary model with Z= 0.008 for ages up to 1 Gyr. For older ages they used the UBV colours of (Searle et al. 1973) and the (Charlot & Bruzual 1991) simple stellar population (SSP) models for the evolution of the V-band luminosity in the age range from 1 to 10 Gyr. They compared their cluster colors with models using UBV and BVR to get the age. They used a value to correct for reddening E(B−V) = 0.13 mag. Chi-squared minimization method: We use the method of (Hancock et al. 2008; Chandar et al. 2010) where the observed integrated colors are compared with the reddened model (SB99) colors using the Chi-squared minimization calculations to get the best match between observed and model colors and hence the age. asadrs@mail.uc.edu

4. Chi-squared minimization method: asadrs@mail.uc.edu

5. Mass of clusters • Galaxies have large masses so they can be studied using statistical measures. • For much less massive star clusters, statistical fluctuations might create serious problems. All clusters in the LMC are less massive than 106 solar masses. • We used MASSCLEAN, a new stellar cluster simulation package to estimate a cluster’s total mass. • We want to know whether the photometric ages are becoming worse when applied to low mass clusters and, if so, how it may be mitigated for future work in this field. asadrs@mail.uc.edu

6. Mass of clusters asadrs@mail.uc.edu

7. Hunter age The correlation coefficient = 0.29 asadrs@mail.uc.edu

8. Chi-square minimization The correlation coefficient = 0.61 asadrs@mail.uc.edu

9. Known extinction The correlation coefficient = 0.75 asadrs@mail.uc.edu

10. summery • Different methods of finding ages give different values of ages. • We would like to know which method to use when. • We need a complete database for star cluster ages that we get the different methods. • …. But are these the only methods? asadrs@mail.uc.edu

11. Future work November2010 Observing some of these clusters to find their age using their spectra. asadrs@mail.uc.edu

12. Questions? asadrs@mail.uc.edu