Friday, June 5, 2009


For-loops have now replaced Fruit Loops in the top 1000 topics on my mind. ;P
Context: I was very happy I got my first for-loop to work today!

I was working on the optimal-aperture project, by plotting magnitudes vs aperture size for a small sampling of objects. It took a little while for me to work out how to code it, and with Beth's help when I had like half a step left, I got some pretty good plots! They show the "light distribution" (reminiscent of the HUDF paper, we later realized) of the stars, with first a rapid increase through the first few apertures, with them leveling off around 20 to 30 pixels. So I chose aperture 8 (of the 11), with a radius at 33.33 pixels.

What was interesting were the objects that didn't level off so quickly, but grew progressively throughout... suggesting perhaps that they are misclassified galaxies. This may be interesting to pursue as a further way to analyze and categorize star vs galaxy.

Using aperture 8, I then went through and made quick work of producing cmds of the North and South fields, for all objects, as well as "galaxies" and "stars". Examining these cmds alongside the aperture 11 ones revealed something interesting: the mysterious cloud of slightly brighter points on ap 11 cmds appears to have migrated up from a slight overdensity at a dimmer magnitude on the ap 8 cmds.

I think this follows from my hypothesis about the galaxies continuing to brighten, after the stars have settled. The dots that remain consistent in the cmds between apertures are likely to correspond to those objects whose magnitude we saw level off on the aperture plot. The objects whose light continued to grow would have brighter magnitudes at larger apertures, and would thus appear to climb up the color-magnitude diagram, as did this cloud of points. Again, this could be further pursued as a method to classify and check whether objects are indeed stars or galaxies.

Continuing To-Do List for next week:

1) Look up RA and Dec (and galactic coordinates) of the two surveys and compare star/galaxy density predictions
2) Look up the Besancon galactic model and compare star/galaxy density predictions
3) Next week- look into using color information to distinguish mislabled galaxies from true stars

1 comment:

  1. Good to-do list. And again, nice catch on the "cloud"! I'm interested to talk about that more later this week.