Flexure Test

General description
Taking the data
Analyzing the data

1. General description

The aim of this test is to determine the flexures of ISIS by:
1- producing a series of dots on the detectors by taking arcs using a narrow dekker (dekker 2 in the standard dekker slide)
2- obtaining these arcs at a series of position angles of ISIS and elevations of the telescope
3- by measuring the offsets of the dots with respect to elevation=90 and PA=0.
It should be done periodically, at least once per semester. This test can last more than 2 hours.

Back to the top

2. Taking the data

The first step is to set up the instrument to run the test and define exposure times and windows:

1- Do the setup as if you were going to use the dichroic
2- Turn off the lights in the dome (not critical, in case some lights are needed during the test
that can last more than 2 hours, try to keep them as lowe as possible)
3- Verify that the standard dekker slide is installed and then put it in the position of the 1.2 arcsec mask
       SYS>dekker 2
4- set readout to FAST and keep the window used to do the set-up.
5- Turn on the CuNe and CuAr lamps
       SYS>complamps cune+cuar
6- take an arc of 10s in red and another of 60s in blue
       SYS>arc red 10 "test"&; arc blue 60 "test"
7- verify that both arcs present well exposed lines (several thousand counts at peak of some dots)
and select another exposure time if needed. Consider that several images will be taken during
the test and if you do not want to expend a long time doing it, the blue exp. time should not exceed 100s.
With low-res grattings 5 and 60s exp. time works fine.
8- Select a small window of 100 pixels width on the spatial direction of the detectors to cover the spectral lines
(eg, window red 1 "[1000:1100,1:4700]" )

IMPORTANT:
Before starting the test the TCS should be setted to computing mode, ask the TO
or the duty eng.!!!!

After doing the setup, for any choosen grating, you should run the script
       SYS>./flexure_isis.csh A B
were A and B are the red arm and blue arm exposure times resepectively, e.g. A=10s and B=60s
(This should work also for the R1200 grattings)
The script basically does the following:

1- Park telescope to Zenith
2- Rotate ISIS (Cassegrain turntable) in a series of PAs (-90 -45 0 45 90 135 180 225 -90) and take
arcs in both arms with the A and B exp. times.
3- On each PA the telescope moves to a series of elevations (90, 75, 60, 45, 30,
and 15 degrees) and on each position takes arcs in both arms.
4- Park telescope to Zenith

A shorter version of the test can be run to check if everything is correct
SYS>./flexure_isis_short.csh A B
This script does the same but for PA (-90 0 90 180 -90) and elevation (90 60 30) only

Back to the top

3. Analyzing the data

To analyze the data we should run the IRAF script "isis_udas_flexure" under the ing package.
We recomend to do that from the observer computer (whtdrpc1).
First mv to /scratch/whta/ISISflexures
Create a directory with the date (e.g. mkdir 20061106)
Copy the data to this directory and the run

        cl> isis_udas_flexure first_image_number last_image_number

As an output the package produces a two files "flexure.dat" and "flexure_table.dat"
with the PA, zenith distance, x-offset and y offset (in pixels).
At the moment the program determines the offsets of the data obtained with
the CCD of the first image, e.g. if the images produced by the flexure test are r812454
to r812560 and the first one is that of the RED arm you should run

        cl> isis_udas_flexure 812454 812560
this will process all images taken with ISIS RED arm, then do
        cl> mv flexure.dat flexure_red.dat
        cl> mv flexure_table.dat flexure_table_red.dat
then the red arm flexures are stored in the flexure_table_red.dat file
        cl> isis_udas_flexure 812455 812560
this will process all images takken with ISIS BLUE arm, then do
        cl> mv flexure.dat flexure_blue.dat
        cl> mv flexure_table.dat flexure_table_blue.dat
then the blue arm flexures are stored in the flexure_table_blue.dat file

Finally, using the gnuplot flexure.gnu script on /scratch/whta/ISISflexures, create plots similar to those
shown below and called flexRED.ps and flexBLUE.ps

        cl> !gnuplot ../flexure.gnu