|Home > Astronomy > AutoFib2 > SA Notes|
DetectorThe default detector used by AF2 with the WYFFOS Long Camera is Red+4. However, it is also possible to mount its predecesor WHTWFC, if there is a strong scientific case that justifies its use.
Red+4 is a 4k x 4k CCD that suppresses the fringing at the red end, and is cosmetically superior to its predecesor, which has been degraded for many years of use.
In the following, we always refer to AF2+WYFFOS with the RED+4 CCD.
Fibre numbering on the CCD frameFibres run from 1 to 150 going from left to right on the display window.
CCD fibre separation is about 22.5 unbinned pixel.
To identify fibres, the fibre number can be overplotted using the ds9 region files:
/home/whtobs/AF2/ds9Reg/af2bin1_red4.reg (no binning)
/home/whtobs/AF2/ds9Reg/af2bin2_red4.reg (binning 2x2)
In ds9 select "Region/Load Regions...", then "Region/Select All" to overplot the labels. You can move the labels left/right using the <- or -> arrow keys.
Spectral range, vignettingWith AF2, and the RED+4 the blue is up and red is down.
On the bottom of the CCD (red side), < 300 pixels suffer from strong vignetting to complete obscuration by the relay mirror. Useful CCD pixels are then Y > 300 (unbinned) for reflection mode.
There is an overall curvature, with wavelength shifting to redder wavelengths in the central fibres, in addition to the expected wavelength shift within every trio of fibres (see sketch below).
In reflection mode, the maximum distance (lowest fibre of every trio on the left/right side, compared to the uppest fibre in the centre) is about 140 pixels, which makes a maximum wavelength shift of some 5% of the total spectral range. The wavelength shifts between two consecutive fibres in each trio is 56.2 pixels.
Currently, a Grating Offset Value of 6.85 degrees provides the required central wavelength in an intermediate fibre, so that some fibres are shifted up to 2.5% toward the red, and the others up 2.5% to the blue. But check it every time you setup a grating.
ResolutionWith any spectrograph configuration, the FWHM of the arc lines is ~1.8 binned pixels (~3.6 unbinned pixels) in both spectral and spatial direction. In the case of sky lines, the FWHM is ~2.4 binned pixels (~4.8 unbinned pixels). The differences between arc and sky lines FWHM is due to different optical path and illumination beam from the sky and from the calibration lamp unit.
Fibre translationThe slit translation to keep the spectra of all the fibres within the CCD area is set to -1300 microns (wslittran -1300). The fibre 75 was used as a reference, it was placed close to the centre of the CCD frame.
Increasing the slit translation value moves the spectrum to left: 1000 units corresponds roughly to the fibre separation (22.5 pixels).
Cryostat alignment and focusingIf the spectrum appears to be rotated anti-clockwise, then you have to rotate the cryostat counterclockwise by approximately two mm for every 100 pixels of rotation in the spectrum.
Regarding the CCD tilt and focus, there is not a clear procedure. The aim is to use the Hartmann shutters, but for the time being we just move the capstans and slit focus.
We can use the following hints, based on experience:
TASKS TO BE DONE ON SETUP NIGHTSThere are several tasks which must be done following each instrument change to AF2+WYFFOS. Some of these are done by the support astronomer, and others are done by the OSA, but it is ultimately the responsibility of the support astronomer to ensure these essential setup tasks are completed following the instrument change.
In the afternoon (by the support astronomer):
At night on-sky (by the OSA and support astronomer as specified below):
UPDATING FILES IN THE WEB AND AF2_CONFIGURE SOFTWAREThe main html documentation is in
Each time that the small_fibres.dat file is changed (e.g. when a fibre is disabled), or the wht_prime.dat file is changed (e.g. after a new mapping field analysis), the new version should be copied from /wht/var/ to /data/docs/Astronomy/instruments/af2/.
The small_fibres.dat and wht_prime.dat files in the local installation of the af2_configure package are symbolically linked to the versions in /data/docs/Astronomy/instruments/af2/, which therefore should have read permissions.
Configurations files used to physically configure AF2 must have been created with the current versions of small_fibres.dat and wht_prime.dat files.
|Top | Back|