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Eclipsing binaries and exoplanet transits

RGN
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Joined: 2010-09-11

I wonder which is the best method to be used to achieve millimag. photometry that is required for instance for exoplanet transits. I have read some papers that recommend defocusing stars so that the effects of seeing are strongly reduced. According to the authors defocusing stars and using integration times between 100 and 200 secs will deliver excellent resuslts, particularly if SNR is very high (e.g. at around 1,000). What do you think?

Gianluca

Gianluca, I have done quite
STHO
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Joined: 2010-09-01

Gianluca,

I have done quite a bit of photometry on eclipsing binaries and exoplanet transits and I would agree, a slight defocus will improve the photometry. I had a student that made a detailed study titled "Purposeful Defocus" in which he performed photometry of the same stars at near the same altitude using discreet defocus positions and indeed there is a sweet spot that can be found based upon your system and the seeing. I have been able to get millimag precision using this method.

I would advise you to test this out for yourself and become familiar with your specific system using M67, the "Henden Field" and compare your results with Arne's published photometry. You can also try using our APASS photometry against your results to see how they compare.

Tom Smith

Dark Ridge Observatory

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484