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WORKING WITH CIRPASS

CIRPASS is a near-infrared (0.9 - 1.8 microns) fibre-fed spectrograph. Two fibre feeds exist: a 490 element integral field unit (IFU) and a 150 fibre multi-object bundle. The large spectrograph is operated inside a freezer working at -40 degrees celsius. The spectrograph camera, the filters and the detector are inside a dewar which is cooled by liquid nitrogen. CIRPASS was used Dec2003/Jan2004 at CASS using the 150 fibre multi-object bundle.
Startup

TCS: Focus:
The best focus is determined taking images using the uDAS TV and examining the images with IRAF.

Autoguiding:
Use the standard uDAS autoguider for CASS with AUTOFOCUS 2500 and AUTOFILT I. This was last started from the orange cetus (whtdas4) window with 'obssys 1', 'startobssys' and 'startag AG6'. No window is required here!
GSS is used for finding guide stars, connect to LPVS3 via LAT and login as GSS. With ICL>PRAG x y command you move the guide probe to the required position. PRAG sends the PROBE command to the TCS, this is essential for correct guiding. Choose a guide star with autoradial larger than 20000 as otherwise the guide probe is vignetting part of the field.

uDAS TV:
The uDAS TV is used for field acquisition and looking at the guide fibre bundle. uDAS TV is best started up from the orange grus (whtdas10) window with 'obssys 1', 'startobssys' and 'starttv AG4'. I used last a window of:
SYS> window AG4 1 "[375:630,280:555]"
The camera can be used as a conventional science camera as far as uDAS is concerned.
SYS> run AG4 2 "focus 98.0"
This command will save the image on /obsdata... (e.g. for measuring best telescope focus using IRAF)
To mark the 6 guide fibres on the AG4 image display load region file /home/whtobs/cirpass.reg.

Preparation

Rotator centre, 7 star calibrate and aperture offset: first night only.
There is no slit reflecting light as with ISIS, therefore use scale 5 and the direct viewing probe (AGCOMP).
Mark the star position on the TV screen (x,y), rotate 180 degrees, mark again and calculate the midpoint (last value was x= 216 y= 291 with CRYOCAM and bin 2x2 for fast readout).

7 star calibrate is done on the rotator center with the rotator tracking turned off (USER> ROT MOUNT xxx).

Using a multi-object instrument it is recommended to define the aperture 0 offset, such the field rotates around the instrument centre. The instrument centre is defined as centre of field plate. The last aperture offset found was X= 2.60 Y= -1.60 (ENTER AP 0 2.6 -1.6)

Observing

Acquisition (first with CRYOCAM, then with uDAS TV):
Move to a bright star in the field and acquire this star using AGCOMP with TVFOCUS 7000 on the instrument center with CRYOCAM.
Next remove the comp mirror (AGMIRROR OUT) and make sure no A&G box mirror is in when observing! Blind to the field center and acquire with the uDAS TV.

XY HANDSET cursor keys, uDAS TV:

       +------+
       |      |
       | <--- |
       |      |
       |      |
+------+------+------+
|      |      |      |
|  ^   | ---> |   |  |
|  |   |      |   v  |
|      |      |      |
+------+------+------+

It is likely you have to re-acquire the same field later or on following nights. Therefore keep a log of the probe coordinates, the X and Y guide coordinates and the CASS rotator position. This will enable you to acquire known fields with the autoguider.

Ask observers about the wavelength of the observation. The acquisition bundle looks through an I-band filter, therefore for acquisition WAVE 0.75 is used. Before guiding change to the wavelength you observe with and try to spot witch way the stars move on the acquisition bundles. You should maintain this offset, however normally you don't notice a difference.

Once the guide loop is closed be aware that tweaking rotation is only peformed correctly using the TWEAK command!

Data Handling

Done by observers on their own data acquisition system.


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