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Re: How to keep FITS header when stacking?

Posted by Luca on Aug 14, 2017; 4:11pm
URL: http://astroimagej.170.s1.nabble.com/How-to-keep-FITS-header-when-stacking-tp725p745.html

You're amazing! Thanks. I'm sending you the measurements file right now, but if you want I can also just upload the aligned fits files tomorrow on dropbox once I'm home.

Yes CCD noise settings are correct, or at least they're taken from the camera sensor manual. We're going to test every feature in September to see if they're somehow different from the average:
CCD gain: 1.5
CCD readout noise: 15
CCD dark current per sec: 0.1

I've actually made a huge Excel spreadsheet which calculates all forms of errors for a single star and comparison stars (with some input), and then finds the best exposure time and defocussing in order to obtain the least amount of error per unit time. In this case each image had 10 sec exposure time, and by my calcs the scintillation noise was dominant. Only considering that, the error bars should be 3x the size that AIJ finds. Then I also made an estimation of the correlated noise (1.3 mmag or so), and that should increase the overall error by quite a bit as well.

P.S. I find that most of the times, with the setup we have, it's better to keep the exposure time below 60 seconds (even more so because more images you get for the transit, less error you have on the calculated parameters), so the scintillation noise is a big issue that doesn't go away with less bright targets.
This is the errors (sigma mag) I find for HD189733b (7.7 visible mag!) using 3 comparison stars, over exposure times: