Following the removal of SCUBA2 from the dish and the adjustment of the central bearing, we have carried out an inclinometry run followed by an update of the RxA pointing model. The result of this engineering work was initial AZ/EL pointing offsets of ~25"/15". The plot below shows the systematics introduced by the changes. A new model was immediately required to return to nominal pointing performance.

As an initial step, an intermediate model was generated with just 10 data points to correct the gross offsets. This had the effect of improving the fits of the subsequent data collected and speeding up the acquisition time.

Following the installation of the intermediate model we were then able to start the official pointing run. Unfortunately at this stage the weather lost stability and was extremely variable during the 3.5 hour pointing run.

• &tau_225GHz &asymp 0.12 (00:15 HST) - start of run
• &tau_225GHz &asymp 0.19 (03:15 HST)
• &tau_225GHz &asymp 0.14 (03:45 HST) - end of run

During the run we collected 28 useable data points. A full 7-parameter fit with TPOINT was carried out and a new model was installed at ~04:00 (HST) on 20090228 with residuals (dS,dZ) of 2.0, 2.6 respectively.

   UT Date     FE     No.    CA  +- dS      IE  +-  dZ
                               (daz)          (del)
   20090227    A      24   -28.6 +- 2.0    -7.4 +- 2.6 
 

The result is displayed below;

CHECKING THE MODEL
The plot belows show the RxA pointing for data for the 3 nights following the installation of the new model.

        UT Dates        FE     No.    CA  +- dS      IE  +-  dZ
                                         (daz)          (del)
   20090228/0301/0302    A     28    +0.8 +- 1.7    -1.1 +- 2.4 
 

20090305
There appears to be a systematic emerging in dZ (see central plot). A correction was applied to the model to correct this giving;

        UT Dates        FE     No.    CA  +- dS      IE  +-  dZ
                                         (daz)          (del)
   20090228/0301/0302    A     28    +0.8 +- 1.7    -1.1 +- 2.0 
 

This modification was installed on 5th March at 16:50 (HST).