to derive cluster dispersal times, relate cluster to star formation events in the galaxy, or estimate their impact on the surrounding interstellar medium, the ages of individual clusters must be accurately measured. This technique has a long history in clusters within the Milky Way (see, for example, Russell 1914) and has recently been extended to massive YMCs in nearby galaxies (e.g. 2011) or the equivalent width of recombination lines (e.g.
If 100 pounds of a material with a half-life of 500 years is deposited, then 500 years later, 50 pounds will remain. By comparing the amount of the parent material to the amount of the daughter material, geologists can determine how old radioactive material is.
This chart shows what percentage of a radioactive material will remain after certain numbers of half lives.
The localization of this technique to the near-IR promises that it may be used well into the future with space- and ground-based missions optimized for near-IR observations. 2007) to a grid of models (age, extinction, metallicity) that follow the evolution of the spectral energy distribution of a simple stellar population.
In order to study a population of stellar clusters, i.e. The second uses resolved photometry of individual stars in order to make colour–magnitude diagrams (as a proxy for the more physical Hertzsprung–Russell diagram) in order to compare with theoretical stellar evolutionary isochrones. The third category is to use some features of the YMC, such as surface-brightness fluctuations, the size of the bubble created by the YMC in the surrounding interstellar medium (ISM) (e.g, Whitmore et al.
As discussed before, the assumptions influence the interpretation of the data.