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Sunday, April 20, 2008

 

Fun with Phase Folding

I'm still trying to figure out how to reduce the variability of intensity measurements in the STEREO Secchi instruments so as to see if I can pick up exoplanet transits. One way is Phase Folding, as used by various groups to study stellar variability. What one does is observe several transits, then alignig all the values with respect to the transit maximum. As the transit maximum will drift, the pints will not align perfectly, so you don't reduce variability per se, but they will define the peak more clearly. Compare the image here, made of 3 passes of Algol phase folded, to the Algol peak defined here on a single pass. Algol is an easy target, but it lest me practise my alignment without hunting for a week trying to find the blasted star. Not also the subsidiary dip. The main dip is when the cool dim star passes in from the the bright star, the subsidiary dip is when the cool dim star is hidden behind the dim star.

There's still a few issues. Even for a bright star like Algol, it's measured intensity is quite different between satellite runs, and I have no clear idea of how to normalize this. Also, the more runs you can fold in, the better your sensitivity. However, 83 Leonis has a long period of 17 days, and you only get two passes in STEREO per year. Still, I'll have another go with Phase folding and see what I can come up with.

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