This recipe is a simple example of reducing CCD data. It uses the xreduce easy-to-use GUI (Graphical User Interface) to the CCDPACK package (see SUN/139). xreduce makes the reduction of CCD observations very straightforward. Using xreduce you can follow various routes to reduce your data. However, most of them are fairly similar and involve the following steps:
The recipe given here corresponds to one simple route through the data reduction. xreduce is described further in SUN/139, especially Section 4, How to reduce your data now. Some additional illustrated examples have appeared in the Starlink Bulletin.
If you have not already set up for working through the recipes then you should do so now. The procedure is described in Section . Then proceed as follows.
The first command starts CCDPACK, the second starts the xreduce GUI. The ampersand (`&') runs xreduce as a detached process, so that you can continue to issue Unix commands from the terminal window.
The main xreduce window should appear, as shown in Figure . Extensive on-line help information is available from most of the xreduce windows, to the extent that it is virtually an `interactive cookbook' in itself. Simply click on the Help menu in the top right of the window. Several options are available: for assistance on using the current window choose the On Window option. The help information is presented as hypertext displayed with a Web browser (Netscape by default).
The underlying purpose of xreduce is to gather sufficient details of your data to define how they are to be reduced. Basically it needs to know: which of the CCDPACK options you plan to use, a few details about your CCD frames (such as the extents of any bias strips) and the names and directory specifications of each of your various types of data frames (bias frames, flat fields, target frames etc). In order to make specifying the details of the CCD frames easier xreduce has a list of commonly-used chips which you can choose from. If the instrument that you used is not included in this list then you can enter the requisite details manually.
Figure shows the window as it is created by default. A useful trick is to expand it horizontally so that the file names and descriptions are more easily visible. Some of the CCD descriptions end in `(setup)' and others in `(table)'. xreduce knows more about the former than the latter. The option chosen here ends in `(setup)', so full details are available.
Once you have selected the detector click on the OK button.
Now click on the CCD Characteristics button in the main window. Again the defaults are acceptable, so click on OK.
Click on the Manual Organization button and a window similar to Figure should appear. The example data comprise only bias frames, flat fields and images of target objects, so click the three corresponding buttons in the list of Frame types present: in the top half of the window. Ensure that these three are the only data types for which the buttons are set.
The defaults can be accepted for the other options in the lower half of the window. Simply click the OK button.
Repeat the procedure for the flat field and bias frames by clicking on the FLAT and BIAS buttons (in the row towards the top left of the window) respectively and proceeding as before. The flat fields are in subdirectory flats and the bias frames in bias.
Once you have specified the files for the three types of frame click the OK button. A window should appear briefly showing the message:
Setting data descriptions, please wait
and you will be returned to the xreduce main window.
checking possible debiassing methods please wait
and then be replaced by a window similar to Figure . For the example data all the defaults can be accepted, so just click the OK button.
performing reduction scheduling please wait
should appear briefly and be replaced by one saying:
Reduction started. The output will be logged in file "xreduce.log".
Click on the OK button.
|CCDPACK.LOG||CCDPACK log file|
|MASTER_BIAS.sdf||master bias frame|
|MASTER_FLATNONE.sdf||master flat field frame|
|xreduce.csh||xreduce reduction script|
|xreduce.log||xreduce log file|
Some files have also been created in the targets subdirectory:
are the de-biassed target images and:
are the de-biassed, flat fielded images: the final product of the data reduction. They can be examined, for example, with GAIA. Type:
gaia targets/ngc2336_r_2_db_fl.sdf &
After setting the Auto Cut level, Magnification and colour table (see the recipe in Section ) the image should look something like Figure .
Note that script xreduce.csh is not deleted because it is interesting to compare it with the commands issued in the following recipe.
The 2-D CCD Data Reduction Cookbook