Astrophysics Group, Cavendish Laboratory, Cambridge, UK.
OOF Holography Recent Results
This page contains the more recent measurements with our new OOF Holography system. Previous measurements are available at previous results.
The latest Out-Of-Focus data were taken with SCUBA on 11th February 2003. These were the first maps with non-azimuthal chop throw which could be introducing some systematic errors. Also several of the pixels on the array were flagged as bad in the reduction. The initial results of our analysis, shown bellow, indicate that the largest errors are related to n=2,l=0 and n=4,l=0 Zernike polynomials (i.e. the "defocus" and "spherical aberration" terms). As these could be easily due to non-dish errors, we have also produced a map of the dish with there errors taken off. We fitted for Zernike polynomial up to and including order five.
The following data from the JCMT was taken on 23th of April 2002. The results of our analysis are shown below. We have flagged the pixel "b13" of the long-wave array as bad -- there is probably at least one more noisy pixel on the maps.
From our analysis of the GBT data we have learned that excessive smoothing in the regriding stage of data reduction can have a systematic effect on illumination and surface. Therefore we have experimented with reducing the smoothing to the minimum. The second set of results below shows an analysis with extremely small support for each pixel. Interestingly the best-fit surface shows an inversion with respect to the first set. We think this is due to loss of crucial information in the bad pixel.
The following were all taken on the morning of the 1st of January 2002:
These beam maps were taken on 3/10/2001, using Mars as the source. Mars at the time was around 10 arcsecs in diameter so these maps provide a test of ability of the software to cope with extended sources. The results are summarised in the following plots: ~~available soon - see previous results page for now~~
We have recently obtained some OOF data from the Green Bank Telescope operated by the NRAO in the US. the results are shown here.