Cluster Notes

Notes for Teachers: Age and Distance of a Stellar Cluster

This lab works best if they've actually gotten to take their own pictures.
If you decide to try it with a different cluster, be sure to get a finding chart of which stars in the field are actually part of the cluster and which are not (this can be calculated from the proper motions). This is not so difficult for globulars as it is for open clusters, but the photometry can be trickier...
Be sure to remind students that the isochrones do not depict the evolutionary tracks of individual stars. They will often get confused about what they are looking at. It is a similar misconception to the one where they think that stars evolve "along" the main sequence. Sometimes it helps to ask them why the older isochrones are at the bottom right corner of the graph (massive vs. light stellar evolution). Also, what happened to the stars that used to define the younger isochrones... (These are hard questions that they'll have to think about for a while since they're generally not quite comfortable with the H-R diagram at this point...)
10 transparencies of the isochrones can be found in the filing cabinet in the lounge---please return them to their folder when you are finished, or make more if you want to send them home with students. The original is also located in this filing cabinet. Use this only to make another copy!!!! Return it immediately to the drawer.
A graph paper template can also be found in the drawer in the filing cabinet. The critical thing is that this graph should be the same size as the one that the isochrones are drawn on, and the tick marks on both of the axes must have the same spacing. Otherwise, the Main Sequence will never line up, and the isochrones will be impossible to match with any accuracy. Make photocopies of the graph paper template, and return the extras to the cabinet for the next teacher to use.