Wednesday, May 19, 2010

Adam's Thoughts...

Adam Myers got back to me about the differences in our thresholds. He thinks that my problem is that I am setting the thresholds with objects that are in the stellar locus, so this is making my thresholds higher than they should be (from 5/19 email re: Testing Likelihood):

~~~~~~ guess is that your thresholds are so high because the area between RA = 320 and 321 degrees has one of the largest gradients in stellar density of anywhere on the sky (see the attached quick-plot).

If you compare you threshold in this range to the other RA strips you should find that it is grossly deviant

e.g., my numbers are likelihood v2:

0 < RA < 1....threshold at 20 fibers per sq. deg. = 0.468797
320 < RA < 321....threshold at 20 fibers per sq. deg. = 0.999961

In fact, 320 < RA < 321 dominates the counts to the extent that you don't even really *see* the other strips in RA in your test. Taking the first 240 objects over your 12 degrees of strips (i.e. targeting at 20 per sq. deg.) I find that 90% (215 out of 240) of them come from the 320 < RA < 321 strip. So, that's your problem there. This is why I set thresholds over large representative areas, preferably outside of stripe 82. Although, I think you'd be safe to continue doing what you're doing if you stick to, say strips in the range 350 < RA < 60.


So it looks like I need to try again, setting the thresholds with a different sky region (away from Milky Way). Results to follow.

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