This release corrects the problem of erratic guiding and insufficient flexibility when using the UES slit. The full width of the slit could not be used, and closed loop performance was worse than open loop tracking in some conditions. The guide window would track unexpectedly due to seeing variations, and lose the guide star.
The improvements will also affect the other configurations. These have not yet been tested and released.
Release note summary
4.1.28:
fix to ?net command not to poll system and window border checks.
4.1.29:
4.1.29: as 4.1.28 but better coded.
4.1.30:
4.1.30: Several UES operational problems worked on.
4.1.31:
Guide window bounded to fibre or ccd underscan; star allowed to
be anywhere in window.
4.2:
UES slit guiding problems: development version at RGO.
Conventional weighted sum centroiding.
4.3:
UES improved version with slit filling and gaussian
cross-correlation centroiding routines.
This version has three major differences from previous versions. The centroiding algorithm now correlated a gaussian profile with the X and Y profiled of the stellar image. This has improved sensitivity significantly. The slit guiding algorithm now splits the slit up into two halves, above nd below the notional slit centre and centroids these in turn. If enough signal is present in both halves, the combined profile is recreated using an slit filling algorithm which attempts to recreate the star profile between the peaks of the profile in each half. This linearised the system transfer function leading to much more stable guiding performance in high signal to noise conditions when there is signal on both sides of the slit. The guide readout window can now track to any part of the readout fibre area, irrespective of the position of the star within the readout window. This allows the star to be at any position in the slit ad the guide loop will still work. CCD underscen limits are still valid, restricting usage to away from the edge of the CCD, but the useable area is significantly larger than before. Finally, the tracking of the guide window is triggered by the star being nearer to the edge of the window, rather than not being in the centre, thus allowing the dead band in the centre of the window to scale with window size. The window tracking is disabled by default in this version by default, as this function was rarely used, and the potential for losing guide stars given an odd star sample position was very real in some conditions.
This system was extensively tested through its UtilNet interface and many small problems rectified, improveing robustness. The guiding performance was fuond to be significantly better with limiting magnitudes of 15 on the slit and 16 on the off-axis probe judged to be acceptable.