Theli-Forum

I know the sequence of processing for R,V, B, Halpha data.

What is the sequence of processing for IR-data?
Where can I read about it?

Hi Oleg,

I think you should have a look at the official Theli website.

http://www.astro.uni-bonn.de/~theli/gui/

In this forum you only find amateur astronomers and I did'nt know anyone who's imaging in the IR band.

Or you ask Mischa for help

Regards

richard

Hi together,

this is a forum for Theli, so all ploblems with Theli can be discussed, no matter if professional or amateur

Thomas

Hi,

of course !
But I meant that nobody here works with IR Data. Therefore there's no one with experience in processing IR Data except Mischa !

Regards

Richard

There are currently no instructions about near-IR processing on the THELI website. Most astronomers who have near-IR data have reduced it before with some other software and are therefore familiar with the concepts and problems, and can dig their way through THELI without much help. For a newbie, however, this is totally different.

Nevertheless, some information is available on the THELI homepage. Oleg, please read sections 9, 8.5.4, 10.4, 10.7, and 15. Which instrument are we talking about? HAWK-I?

This is about what I answered Oleg in an email a few minutes ago:

In a nutshell:

(*) you have to create a superflat, probably with high DT=10 and DMIN=10

(*) if the exposure sequence is longer than about 30 minutes, you have to set "window size" to 2 or 3 in the "create superflat" menue ("calibrate data")

(*) if window > 0, then select "subtract" from the popdown menue appearing right to it; if window=0, then go to the superflatting section, and click on 'subtract superflat' and 'rescale fringe model'

(*) if you have fluffy small targets (galaxies), or very crowded field, you must do a 'collapse correction', selecting 'mask OFC images (2 pass IR subtraction),
to create better object masks. then delete all OFCUC images, restore the images from OFC_IMAGES, go back to 'calibrate data' and re-run the 'create superflat' step, with the same window parameter.

after that, you should have fairly flat OFCU images and can proceed as normal.

most likely things are more complicated because you are processing pretty targets, i.e. large objects for which you cannot create a sky model from the data itself.
to that end you probably (hopefully) have so-called "offtarget" or "sky" images, i.e. pointings to a blank sky field. you must separate these from the normal SCIENCE exposures and dump them in a separate directory, which you enter in the OFFTARGET field under 'initialise'.
in that case, create the superflat from those images only, and when subtracting it under 'superflatting', make a tickmark next to 'use oftftarget superflat'.

i strongly recommend you try with a boring distant galaxy or open cluster field first to see all the bad effects that can happen in the near-IR.
once you have understood what you are doing, move on to the pretty targets.

best (i'm impressed you are diving into this!)

mischa

mischa hat geschrieben:There are currently no instructions about near-IR processing on the THELI website. Most astronomers who have near-IR data have reduced it before with some other software and are therefore familiar with the concepts and problems, and can dig their way through THELI without much help. For a newbie, however, this is totally different.

Nevertheless, some information is available on the THELI homepage. Oleg, please read sections 9, 8.5.4, 10.4, 10.7, and 15. Which instrument are we talking about? HAWK-I?

Many thanks!

WFI on 2.2 m telescope MPG/ESO

oleg hat geschrieben:

mischa hat geschrieben: Which instrument are we talking about? HAWK-I?

WFI on 2.2 m telescope MPG/ESO

Aaaah! Then everything is much easier and you can forget about (almost) everything I said. This is not near-IR data. The near-IR is between 0.9-2.5 microns, covered by YJHK filters.

In that case you can proceed as normal. If your OFC images exhibit fringing (i-band, z-band), you have to create a superflat (window=0), and then, in the 'superflatting section', do a 'process superflat, and a 'defringe data' (using rescale fringe model).
note, however, that this will only work properly if your field is largely empty. otherwise, you have to go to the archive and, ideally, find i-band images of a blank field taken in the same night (good luck with that).

best regards,

mischa

My first result of the IR-data defringing.

Hi Oleg,

oleg hat geschrieben:My first result of the IR-data defringing.

that is insufficient
The (likely) reason is that the DT parameter for the creation of the superflat was too low. Try setting DT=5...10, and run it again.

Correcting fringes is often an iterative process, depending on how crazy the atmospheric airglow was that night.
Keep us posted!

mischa

Result for DT=5