Central bearing measurement

The last measurement ( 981213 ), showed the empirical to be overcompensating by about 3", and this new work shows little change.

Today, we tracked 0605-157, a 3Jy blazar, using the SCUBA map16 method, and with the empirical corrections enabled, from (az,el) = (121/28) at 19:02 HST to (131/38) at 19:59 :

This wasn't the best choice of target -being so weak - but it was the only one available. As a result, the noise in the data is considerable, being 1.4" rms in del, and dominating the 0.6" contribution from the seeing. Taking account of the slight baseline trend in daz, the azimuth residuals show about a peak-to-peak error of about 6" centered at (125.6,33.4); with any asymmetry probably being merely an artifact of the noise. The sense of the residuals is that of an overcompensation by tel_empirical. The current full amplitude of tel_empirical is 14.3" (at the horizon) so the amplitude of the defect at the horizon now is 14.3" - 6"/cos(33.4) = 7.1" (peak-to-peak).

The location and width are within 0.2 degrees of those expected,

The new data are added to the historical record .