Re: Measuring a huge amount of images

Posted by PetriKehusmaa on
URL: http://astroimagej.170.s1.nabble.com/Measuring-a-huge-amount-of-images-tp959p961.html

Hi Karen,

Thank you for your reply. I'll try be more specific this time :-)

Telescope pointing precision is good, pointing error is mainly +/- 1 arcmin. All images are plate solved and calibrated.

Then the hard part.

Atmospheric transparency is pretty stable. Our observatory is at 2500 meters above sea level in Atacama Chile. But of course there are some fluctuation because these images have been taken during two years time period.

The telescope is keeping its focus pretty well even if temperature is changing during the night. Focus routine is done by FocusMax for the filter been used for imaging so no filter offsets are being used. Focus run is done every time before starting the time series.

I'm currently using 8 comp stars which have approx. the same brightness as target. All of these stars are available for the whole stack of images. One of the problem seem to be longterm brightness and its fluctuation. Also meridian flips are causing these fluctuations.

--"If you do the photometry in one run, and then chop the measurements table on night boundaries and copy the header line to each file, you can then load them into AIJ as if they were done separately. Then normalization and detrending of each night could be done separately in AIJ."

How do I do normalization and detrending afterwards? And should I do the one run photometry without detrending and normalization (so 'Fit Mode' and 'Norm/Mag Ref' off) for all stars (target and comp stars)?

And then I need to chop individual nights off from the big file and for each night I need to detrend meridian flips and for transits/eclipses choose fit mode and normalization regions?

For target I have used AIRMASS, tot_C_cnts, Width_T1, BJD_TDB and Meridian_Flip detrend parameters. For comps stars I have used AIRMASS and BJD_TDB.

Is this about right? And after detrending/normalizing all individual nights separately, I should then have T1 data normalized through out the data sets and can then rely on those numbers to do further analysis of the whole data?

Even though I have a pretty stable imaging system, the end result still seem to suffer some systematics which I don't seem to be able to even out. I've been playing with aperture, number of comp stars and detrending parameters without success.

I have data from about 200 nights, so chopping data into individual files for each night is a mighty task.

Petri