|
|||
| Joint Astronomy Centre |
|
|
|
| Show document only |
|
||||||||||||||||||||||
|
____________________
|
||||||||||||||||||||||
|
State of the central bearing problem unclear from recent tracking data :During a SCUBA2 run on 970801, particularly notable for good optical skies but appalling opacity (tau_230 = 1.0), Uranus was tracked for about 1 hour from (az,el) = (233,30) to (244,12). A 10 minute gap in the datastream exists when the SCUBA queue stopped. It was only as I edited a previous report on the monitoring of the central-bearing problem, that I realized that I had probably taken these data with the TEL_EMPIRICAL correction left turned ON. This is not a disaster, but severely hampers estimating the functional form of the glitch . The data-stream shows increasing noise as the source sets, and structure at the expected azimuths that is somewhat significant. By comparison with the original data upon which the empirical correction was based, we would expect almost the full deflection; +6 near az=239, -6 near az=241. In these new data, the correction appears to overcompensate the actual effect - by about 2" in each direction - although this is close to the seeing noise at these low elevations. The effect of the glitch may be greatest at these low elevations, but it is clear that data from higher elevations suffice and avoid these particular problems. I shall make requests of observers to make similar observations in order to continue the monitoring of this problem - they will stress the need to ensure that TEL_EMPIRICAL is OFF. I apologize for this bungle and the need to repeat the test so soon. imc 970804 |
