Example 3: NGC 3766 analysis, part c

So far, we’ve passed over two steps in the Clustermancer analysis: Archive Fetching and Results Summary. Example 3 will help you complete your analysis of NGC 3766 by adding in these steps.

  1. Open Clustermancer. Your browser should still have all your data, field star removal and isochrone parameters loaded, just as you left them in Example 2. If not, please work through Examples 1-2 so you have everything as you left it at the end of Example 2, step 4.
  2. Click on Archive Fetching. You are now going to load photometric data from some all-sky catalogues.
  3. Click the Add Catalog Stars button.
    • If you’ve done a good enough job setting your field star removal constraints, so you have reasonably narrow ranges in proper motion and distance, you should be able to fetch using the maximum radius, which is the default.
    • In the Catalogues drop-down, select GAIA, 2MASS and WISE. Do NOT select APASS, as APASS contains some of the filters in your data set and the data will be combined with your data.
    • Click Test Radius, and if there are fewer than the maximum number of stars the program will allow, you should see Fetch Data appear as an option. If so, click Fetch Data. If not, you will have to go back to the Field Star Removal step and tighten your proper motion and distance constraints, then come back and try the maximum radius again.
  4. Once Catalog Fetching is complete, you will see a new set of columns appear showing the number of cluster stars and field stars within the set radius in each of the catalogues you’ve fetched from.
  5. Go back to Field Star Removal and refine your proper motion and distance constraints. When you are happy with your constrains (refer to Example 1 for a refresher), move on to the Isochrone Matching page.
  6. On the Isochrone Matching page, close any graphs you have open and create an HR diagram with BP set as “Blue”, RP set as “Red” and RP set as “Lum”. Set the Max Error value to 0.05, and select Frame on Data.
  7. Refine your isochrone parameters, ensuring to fit model to the denser data at the bottom of the main sequence, ignoring the unresolved binary stars.
  8. Do not focus on any particular stars (e.g. the two red giants) to the detriment of your overall main sequence fit. Remember: you are working with real data and imperfect models here, and there are many factors that can lead to imperfection in your fit. The goal is to find a set of parameters that fits the data set overall as well as possible.
  9. When you are satisfied with your model fit, save the graph as a PNG and move on to the Result Summary page. Here, you will see several derived values listed based on your analysis: number of stars, physical radius (which comes from the angular size of the cluster and its distance), mass (which is calculated from the proper motion dispersion and radius of the cluster, i.e. based on the orbits of the stars within the cluster), among other parameters. Several graphs are also displayed, including an image showing the cluster’s location within a representative barred spiral galaxy that looks something like our Milky Way might look from a distance. Click the CSV button at the bottom-left and save a copy of the parameter values you just derived through your analysis.