a study of the ages of large magellanic cloud star clusters randa asa’d university of cincinnati...
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A study of the ages of Large A study of the ages of Large Magellanic Cloud star clustersMagellanic Cloud star clusters
Randa Asa’d
University of Cincinnati
Adviser: Dr. Margaret Hanson
Bucuresti 23 Septembrie 2010
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)
Introduction
Hunter Catalog: (Hunter et al. 2003) compares the data with the Starburst99 (Leitherer et al. 1999) evolutionary model with Z= 0.008 for ages upto 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 minimizationcalculations to get the best match between observed and model colors and hence the age.
Photometric age
Chi-squared minimization method:
Cluster name
(U-B)_obs (B-V)_obs
Model Age (U-B)_mod (B-V)_mod reddening
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.
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?
Future work
Observing some of these clusters to find their age using their spectra.
November2010November2010
