Pointing corrections and final map creation

Before we create our final rebin, we will still need to calibrate the map (Section ) and correct for pointing drifts that occurred over the map. Since we have only dealt with a single map so far, we omit the calibration stage and proceed to correct for pointing drifts. To do this we reduce the closest pointing observations before and after the map in the same way as we reduced our map, but with minimal despiking and regridding the pointing map in az. These pointing errors we find have to be negated in the task change_pointing. For scan 86 I find one pointing done on the star itself before the map (#81), and none afterwards. The final pointing errors of # 81 are DAZ/DEL = 0.38''/+0.33'' at an LST of 9:26 as deduced from the FITS header of that scan. These errors are the residual from on-line pointing corrections and off-line data reduction of scan 81. If we treat our map as if it was a pointing observation we find pointing errors of +1.52''/+0.12'', which we apply directly after negating the sign as shown below. Instead of choosing a time halfway through the map, we have to take the LST time at the end of the map. This is kind of cheating, because we derive pointing from the same objects that we are supposed to correct the pointing for, but here we do it only to illustrate how pointing corrections are done.

% change_pointing
IN - Name of input file containing demodulated map data 
/@i86_lon_sky/ > i86_lon_clip
SURF: run 86 was a MAP observation of IRC+10216
SURF: observation started at LST 9 41 05 and ended at 9 50 09
SURF: no pointing corrections found

CHANGE_POINT - Do you want to change the pointing correction data > y
POINT_LST - The sidereal time of the pointing offset (hh mm ss.ss) 
/!/ > 9 26 
POINT_DAZ - The azimuth pointing correction to be added (arcsec) > 
-0.38
POINT_DEL - The elevation pointing correction to be added (arcsec) > 
-0.33
POINT_LST - The sidereal time of the pointing offset (hh mm ss.ss) 
/!/ > 9 50 10
POINT_DAZ - The azimuth pointing correction to be added (arcsec) > 
-1.52
POINT_DEL - The elevation pointing correction to be added (arcsec) > 
-0.12
POINT_LST - The sidereal time of the pointing offset (hh mm ss.ss) 
/!/ >

We can now run the sky noise corrected, despiked, and pointing corrected data through rebin to obtain our final map i86_lon_reb. Looking at the map, we can see that bolometers, which we knew were noisy still can be seen, but since we do not have any additional data sets to add to the map, we will leave the map as such. The pointing offsets, as determined with centroid give pointing offsets of -0.18'' in RA and 0.0'' in Dec, suggesting that the pointing corrections worked quite well.

Now we would do the short array in the same way either by re-running scuquick or by starting with the SURF task extinction. We now run extinction on i86_flat, which was created when we reduced the long array, and which also contains the flat fielded data for the short array.