GIRAFFE

The SAAO Grating Instrument for Radiation Analysis with a Fibre Fed Échelle - GIRAFFE - consists of two components:

(i) The head which is mounted at the Cassegrain focus to collect light from the star and direct it into the fibre;

(ii) The spectrograph, constructed on an optical bench in the Coude room, in which the light emerging from the fibre is dispersed and recorded by a CCD camera.

The CCD camera is controlled by a PC in the observing room. The software, called QUARTZ, has the task of setting the exposure time, reading and displaying the CCD image and also controlling various components on the GIRAFFE head, such as the arc lamp and flatfield lamps. At the end of the exposure the FITS file is transferred to the server and can be displayed and reduced via the thin client.

There are four PCs that the observer will use:

1. A Linux PC called giraffe running QUARTZ.

2. A thin client system for data storage ltsp.suth.saao.ac.za.

3. A laptop running a LabView program to display the APD counts, i.e. monitor the light intensity emerging from the fibre.

4. The Linux TCS PC for acquisition and autoguiding.

Data reduction Software for Giraffe

The technicians would have set up the PC running QUARTZ in diagnostic mode. You need to exit from this and start the software in your own directory.

• Click Exit in the top right of the QUARTZ window, and answer No when it asks you to save a file.

• In a terminal, navigate to /data/ccd, create your own subdirectory, change to that directory and run QUARTZ from there:

cd

mkdir xyz

cd xyz

new_quartz

When prompted, select MUS1 from the pulldown menu, then select Local Setups and giraffe.gir, Ready and OK.

Each GIRAFFE run is assigned a run number, QUARTZ will prompt you to enter. To determine your run number, look in the GIRAFFE log book located in the 1.9-m dome book rack and look for the last entry. Increase that run number by one. If you are a returning observer and wish to use the same directory, you will need to change your run number by deleting the file disk.file from your directory.

At this stage QUARTZ will spend some time initializing the CCD controller and checking the status of the GIRAFFE head. To check that things are working, you can read out the CCD by selecting the Read CCD item from the CCD drop-down menu. This will display information regarding the bias reading and the maximum CCD count.

1. Filling the cryostat

After filling the cryostat, you must wait 30 mins before beginning observations.

A technician will fill the cryostat at ~08:00 and ~16:00 (check on the log outside the Coude room that this has been done before you start observing). The observer must fill the cryostat either at ~19:00 and at the end of the night (avoiding the need to stop during observing), or at ~00:00, whether or not observations have been made.

The cryostat is filled from the dewar outside the Coude room. Check the pressure of the dewar - it should be ~10 bar, and must not exceed 15 bar. Open the right-hand blue tap to start filling, and watch the cryostat. Close the tap when liquid nitrogen starts to drip out of the cryostat.

The CCD "tank" temperature should be ~180K, and the "sink" temperature ~79K. The temperatures are displayed toward the bottom of the QUARTZ window.

Even in bad weather, the cryostat must be filled during the night. The last filling for the night should not be done before midnight.

2. Instrument setup

The instrument is controlled by the QUARTZ software on giraffe PC.

2.1 Starting the software

1) Log on as ccd (usual password)

2) cd to working directory

3) Enter command: new_quartz

4) In the pop-up CCD menu, select MUS1

5) In the second pop-up window, select Local setup files → select giraffe.gir → Ready → Ok

2.2 Initialising the prisms & filters

Do this at the start of the run, using options available by clicking on the “Init” button at the top right of the QUARTZ window:

1) Select “Init” → “Find reference” and wait for “Finding reference...” window to close

2) Select “Init” → “Define red” or “Define blue” depending on the prism you wish to use and enter prism position

3) Select “Init” → “Red/blue position go” and wait for “prism movement” and “detector motion” messages to clear

4) Check and note down the prism position in the “Prism” status box at the bottom of the QUARTZ window.

5) Select “Filter” → “Init” at start of run & before any filter change

6) By taking an arc (follow steps 1-2 in Section 4.1), check the resulting orders are correct and spectrograph focus is good (see Section 5).