Wavelength Positioning and Throughput Checks

Wavelength Positioning and Throughput Quick Checks

General description
Taking the data
Analizing the data

1. General description

The aim of this test is to provide a tool to the SA to:
1- do a fast check of the setup
2- keep a control on the throughput of the spectrograph and the accuracy of the central wavelength setup.
3- keep a control on the CCD bias level and RON.
It should be done by the SA every time the setup of ISIS is done.

The basic idea is to take arcs using the same configuration (depending of course on the grattings used) immediately after the setup of ISIS is done, and bias.

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2. Taking the data

After doing the setup, for any choosen grating, you should run the script:
SYS>isis_script/wltest.isis
BE CAREFUL that if the set up of the red collimator was done with the dichroic OUT (bfold 0),
you should apply an offset of 1000 to it BEFORE runing the script in order to be close to the focus
when the dichroic is in.
SYS>rcoll (actual value + 1000) This script basically do the following:

1- set readout to SLOW and keep the window used to do the set-up.
2- turn off the lights in the dome.
3- select a slit of 200 microns
       SYS>slit 200
4- select the folder position 0 (light stright to the red arm)
       SYS>bfold 2
5- if the set up of the red collimator was done with the dichroic OUT (bfold 0),
then apply an offset of 1000 to it to be close to the focus when the
dichroic is in
       SYS>rcoll (actual value + 1000)
If not forget step 3
6- put the GG495 filter out
       SYS>rfilta 0
7- turn on the arc lamps
       SYS>complamps cuar+cune
8- take care that there are no filter in the comparison box and if necessary do
       SYS>compfilta clear
       SYS>compfiltb clear
9- select the central wavelength to 7503.87
       SYS>cenwave red 7503.87
10- take an arc of 5s
       SYS>arc red 5s "test th&wl"
11- set the central wavelenght to 4510.73
       SYS>cenwave blue 4510.73
12- take an arc of 60s
       SYS>arc blue 60 "test th&wl"
14- take a bias in both arms.
13- if you changeded the collimator focus and plan to observe with the dichroic out
remember to correct it again

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3. Analyzing the data

To analyze the data use the command SPLOT withing iraf

        cl> onedspec
        on> splot image[1]
        Image line/aperture to plot (0:) 100
        (use here the line 100)

You will see a graph that, depending on the gratting, will look like these ones. If it is similar in intensity and position of the lines your set-up is correct. If the intensity is much lower and/or the lines are at much different pixels, you probably put the gratting in a wrong position. Check it.

Zoom the graphs to see better the lines we are interested in using the w and e keys inside splot (see the corresponding graphs here)

        click "w" and then put the mouse in the lower left corner of the region
        you want to zoom, click "e", move the mouse to the upper-right position
        of the region you want to zoom and click "e" again.

Measure the center and flux of the line indicated in the graphs here (it is a line at 4510.73 A and 7503.87 A in the blue and red arcs respectively).

        inside splot, move the mouse to the left position and click "k", then
        move the mouse to the right position close to the line and click "k".
        again. The computed center and flux are indicated in the lower yellow.

Copy both images to /home/whtobs/images_isistests.

Measure the bias level and RON of both bias images using imexam. By cliking "m" at different positions it provides the mean bias level and the std in a box. The expected bias level in slow mode are 1244 and 1386 ADUs for the blue and red respectively and the expected RON is 3.5 ADUs in both arms.

Finally please fill the form and add it to the ISIS Quality Control Data Sheet folder.