A pointing override was requested and granted for last night (UT20020419). The tests that were completed were as follows :

1. Point & focus each of SCUBA, RxA, RxB.

2. With appropriate focus settings, point again 3 times with each instrument in rotation - eg SABSABSAB - to test the repeatability of the TMU positions.

3. Point with each instrument on 2 other sources at different elevations. Ideally choose sources with elevations at 20 50 80 although 30 50 70 will be good.
   This is designed to establish the reality of these recently observed phenomena :
   • that the pointing model, based on SCUBA observations, works OK for SCUBA,
   • that azimuth (and perhaps elevation) residuals for RXA and RXB have strong trends with elevation.

4. Refocus SCUBA and track a bright source with SCUBA for an hour, maybe avoiding transit.

5. Refocus RxB and track a bright source with SCUBA for an hour, maybe avoiding transit.

The results were :

1. (Done)

2.    az      el      daz    del  hh mm ss.s source   FE
     ------  -----   ----   ----  ---------- ------   -----
     188.11  64.13    0.9    4.3  23 43 10.5 3C279    RXB   
     190.50  63.97    4.2    4.1  23 47 25.8 3C279    RXA3I 
     192.42  63.81    1.2    6.1  23 50 51.3 3c279    SCUBA 
     197.06  63.29    0.8    0.0  23 59 23.2 3C279    RXB   
     200.04  62.87    3.5    3.5  00 05 05.3 3C279    RXA3I 
     202.36  62.48    0.1    7.9  00 09 35.7 3c279    SCUBA 
     206.33  61.69   -0.1    2.9  00 17 42.3 3C279    RXB   
     208.26  61.25    3.3    4.6  00 21 49.4 3C279    RXA3I 
     210.53  60.68   -0.2    7.1  00 26 46.4 3c279    SCUBA 
   

   Mean & s.d. for (daz,del) for each FE are (0.5+0.6, 2.4+2.2), (3.7+0.5, 3.0+0.6), and (0.4+0.7, 7.0+0.9) for B,A,S resp.. (Seeing was ~1" at about midnight.)

   Conclusion : Repeatability (of TMU &c) is generally pretty good.

3. This test was not completed as specified, but the goals may be effectively met by the totality of pointing acquired through the night :

   SCUBA	RXA3I	RXB

   (Click on each plot for larger image)

   There are many significant systematic trends in all 3 diagrams :

   • SCUBA : the 2 highest points are 5-10" more negative in az than the other 27 data and suggest a discontinuity or turnover in the del-vs-el plot also. FIT7 can reduce the rms errors to (1.7,2.9) only - indicating that the errors are not intrinsic to the 7-parameter model, and attempts to include the TMU-orientation errors (u3,u4) prevented iteration towards a solution.
     There are basically no model terms that impose a turnover of errors (at el ~70degs).

   • RxA/B : Both datasets show the very strong trend of azimuth residuals with elevation seen earlier. Since the collimation offsets for RxA3I and RxB differed only by 1" or so, the data were combined (to give N=51) and then run through the FIT7 fitting routine. RMS residuals were reduced from a raw value of (2.5, 2.3) to (1.5, 1.9) which smacks of normalcy.
4. Not done.

5. Done - see the RXB plot above. The 31 data points acquired during 1 hours tracking of G10.62 have means and s.d.s in (daz,del) of (3.4+1.0,3.7+1.6).

   Conclusion : Tracking errors seem minimal