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hippke / tls

Transit Least Squares: An optimized transit-fitting algorithm to search for periodic transits of small planets
MIT License
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Question: what does negative SDE mean? #82

Closed jpdeleon closed 4 years ago

jpdeleon commented 4 years ago

TLS yields SDE array as a function of period. In some cases, I got negative SDEs. What does it mean? From your TLS paper:

"An SDE value of x for any given P means that the statistical significance of this period is xσ compared to the mean significance of all other periods."

A negative SDE doesn't mean the period is negative xσ significant, does it?

hippke commented 4 years ago

In pure noise, half the SDE values should be above zero, half below. It's normalized that way. Negative SDE values correspond to signals that are transit-shaped peaks in the lightcurve, phased at that period. There is actually a physical use case for keeping it this way: You can use it to search for self-lensing (see Figure 2 in this paper).

jpdeleon commented 4 years ago

I see. That's cool! Since I am currently interested to look for transits only, I will clip SDE>0 for the meantime. Thank you!