SIMPLE CGS4 REDUCTION STEPS

This document provides a "recipe" for doing basic reduction steps. It is intended as a quick "get you by" guide, not a substitute for the data reduction users guide. Names of menus and menu items are capitalised.

WARNINGS

If you set the data reduction up eg. to subtract a dark and it cannot find a suitable dark because one has not been observed then the data reduction will report an error message and pause.

You need to sort problems out before attempting to resume the reduction - or errors will accumulate. For example the first observation of a set of object-sky pairs must be of type object, and so if the first observation in your group is not reduced because of a mistake in the reduction set up you must re-reduce it in order to get a coadded group of object-sky pairs. This may include having to re-insert observations in the queue - if this happens and you are not sure what to do, pause the data reduction and ask the TO for help.

Getting Started

1) Run up the data reduction using CGS4DR_DEV and answer the prompts.

2) Double click on the "captain starlink" icon to open the plotting window and arrange the windows in a convenient way.

3) Go to the REDUCE menu with the arrow keys and press enter. This puts you in a menu called "DATA REDUCTION MENU". This is the main data reduction menu - all the other menus can be reached from it.

4) Start the automatic data reduction by selecting the item "PAUSE_CONTINUE_REDCTION" (middle of first row of items).

5) At this stage you should be running the EXEC ARRAY_TESTS on the data aquisition, and the data reduction will reduce the bias and darks and plot the results.

6) The dark_tests EXEC loads the data reduction config called "STANDARD_1" which sets the data reduction up for general reduction of observations as follows :

• a) coadd as appropriate
• b) subtract a bias if doing stare observations
• c) apply the default bad pixel mask FPA46_SHORT
• d) Normalise flat fields with a third order polynomial
• e) divide by a flat
• f) interleave according to the oversampling
• g) wavelength calibrate with an estimated calibration
• h) add observations as object-sky pairs into groups if your exec included a startgroup command.
• i) Produce basic useful plots which are :
  • an image of each reduced observation
  • an image of the reduced group every time a new pair is added to it.
  • a cut along row 29 (the recommended peak row) every time a new pair is added.

NB. Because this standard reduction config expects to divide by a flat field you MUST observe a flat at the appropriate wavelength before observing arcs, objects or skys. You are now ready to observe and auto-reduce your data. If you would prefer some other reduction sequence use the SETUP menu to define your own - you can then save this for easy recall later.

How to ratio by observations of a standard:

After observing a standard star, to define the result as a standard for the data reduction to use for ratioing you have to do the following things on the data reduction side :

1) Define it to be a standard by doing the following:

In the DATA REDUCTION MENU, go into the item FILE OBSERVATION. (it is in the middle column of menu items).

Now go into STANDARD.

Enter the file name RG950402_nn, where nn is the group number for the reduced group of the star (ie the observation number of the first observation of the star by your exec), provide a suitable effective temperature (eg 8000), reference wavelength (usually the central wavelength of your spectrum eg 2.2), and which rows to extract. Entering the same value for start_row and end_row will extract just that one row. (eg 29 and 29) When everything is setup PF1 out of the menu. It is wise to extract the standard over three rows, ie rows 28-30. The standard is written to a file called ST950402_nn.

2) Turn on ratioing

After you have done the above steps to label your observation as a standard you need to turn on the ratioing by doing the following:

• Go into the SETUP menu
• select SET_REDUCTION_SEQUENCE (top left).
• Set "Divide_by_standard_source", to YES.
• PF1 out of the menu and then PF1 back to the data reduction menu.
• PF1 out of the menus back up to the DATA REDUCTION MENU.

Notes:

When you have divide_by_standard = yes, the data reduction looks for a file called ST.... at the same wavelength as you are observing the source at. If there is more than one of them it picks the one taken closest in time to your object. So whenever you observe a standard star you have to go through the above proceedure in order to use it for ratioing.

If you change wavelength remember to set "Divide_by_standard_source" = NO in the SET_REDUCTION_SEQUENCE menu until you have observed a standard at the new wavelength and filed it as a standard as above -otherwise the DR will look for a standard at your new wavelength, which of course you havent observed yet and it will then refuse to reduce your observations of the new standard because it could not find and appropriate ST file to divide by.

How to make extra plots of your data:

Anytime the data reduction is not busy auto-plotting you can make extra plots as follows.

From the DATA REDUCTION MENU, Go into the PLOT_IMAGE or PLOT_GRAPH ect., depending on what you want to plot. Enter the name of the file you want to plot, whether or not to autoscale, where on the screen to put the plot etc. by filling in the menu items appropriately - most are fairly obvious.

The name of the file will be RG950202_nn (where nn is the observation number of the first observation in a group - ie the first one your exec took) if you want to look at the sum of the obj-sky pairs. If you have divide by standard turned on then the ratioed file will be called "RG950202_n_dbs"

PF1 out of the menu.

Note that if you get a message saying the P4 task is busy and a beep, just keep trying to enter the menu - it will let you in when the auto-plotting is finished.

How to Make Hard Copies of the plots:

To make a hard plot select HARD in the plot_... menu. The first time you do this a new version of P4 with a hard copy device will be loaded.

To print the file select PRINT_HARDCOPY on the DATA_REDUCTION_MENU. The default file name (GKS_72.PS) and printer queue (SYS$POSTSCRIPT) will be correct. Your TO or support scientist can show you where the printer is.

How to Flag and Observation as Bad.

If you have done eg. a flat and dont want the data reduction to use it because there is something wrong with it yuo can flag it as bad.

From the DATA_REDUCTION_MENU , go into UNFILE OBSERVATION

Enter the name of the file you want to be treated as bad: eg O940502_7 or RG940502_8 (if the problem is with a standard). PF1 out of the menu.

How to Delete an Object-Sky pair from a reduced group

In poor weather if you get a bad object-sky pair becuase the atmosphere changed a lot you can remove it from the reduced group (after it has been added in).

Go into the MANUAL OPERATIONS manual, then into SUBTRACT_PAIR

Enter the name of the observations for the object and sky pairs which make up the pair. Make sure you get them the right way round ! If you dont the DR will report an error and do nothing.

More Information

There is on line help if you type ? on any menu item.

See also the cgs4 data reduction users guide for more details on the above and for more sophisticated techniques. Copies of the user guide can be found in the control room at UKIRT and the JAC terminal rooms in Hilo and at Hale Pohaku. The online CGS4DR users guide now describes Portable-CGS4DR which is not yet in use during observing.