Flexure in the FEROS/WFI Adapter between FibreHead and Technical CCD
A study of the possibility of flexure of the FEROS/WFI Adapter (FWA)
between the FibreHead (FH) and Technical CCD (TCCD) has been made. The
result is that there no significant
flexure.
Description of tests
On 2003-07-17 the telescope was pointed first at the Zenith, then to extreme values of Hour Angle (HA) and Declination (see table 1). At each of the five pointings an image was captured from the TCCD (simply using the Save As... menu item from the File menu in the TCCD RTD window) with the FEROS Calibration Unit (FCU) Wavelength Calibration lamps turned on. The resulting images where then analysed using the FFH-TCCD-FlexureTest-plots.prg MIDAS script. To summarise this procedure, 25×5 pixel regions centered on the expected positions (i.e. those determined at the zenith) of the Object and Sky Fibres are summed over columns and rows separately to produce a 1-dimensional summed flux profile, which is "approximately guassian with a hole in the middle". The minimum of this profile at the center of the Gaussian is interpretted as the center of the fibre.Results
Below are plotted row and column profiles of the flux summed over the five pixels centered on the expected positions of the fibres (left) and also the profile across the single row/column of the expected position of each fibre (right) for both fibres.As can be seen in the plots of the profiles of the summed flux for each of the five pointings (except in the case of the column profile of the Object Fibre at HA=00:00, Dec=+21:00) the center of the fibre moves by somewhat less than 1 pixel , i.e. less than 0.51 arcsec (for the image scale of the TCCD at the time these tests were performed). The solid vertical line is drawn at the position of the expected centre, the dotted lines represent the limits of the aperture (1.8 arcsec apertures and image scale 0.51 arcsec/pixel implies apertures are 3.53 pixels).
