[mmaimcal] [Almasci] B7 Change Requests

[Stéphane Guilloteau]

A 11:39 24/04/2007 -0400, Todd R. Hunter a écrit :
>Hi Richard,
>
>Q1: Yes, you would have to correlate USB with USB and LSB with LSB. In
>order to convert the baseline-based results to antenna-based results, I
>think you may want to include more than the 4 total power antennas in the
>correlation (to have confidence in the solutions).

3 are sufficient, and 4 already provide redundancy.  This is algebraic, and 
not affected
by atmospheric phase noise, so the confidence in the solution is directly 
obtained through
a computation of the statistical errors. But the noise will go down 
(approximately) as 1/sqrt(Nant) anyway.

>This would seem to
>require a re-config of the correlator and the use of some of the other
>ALMA antennas as part of the observation set. Another issue to look out
>for is that there are no Galactic absorption lines in the band toward the
>chosen "calibrator".  (SMA has seen fairly deep, narrow CO absorption
>toward various 3C objects.  My recollection is that this was mostly
>noticed in 2-1, but will likely have some 3-2 component as well.)
>
>A question I have is: will the differing atmospheric transmission (and/or
>ozone features) in the two sidebands affect the solutions?


Yes, indeed. One of the main difficulty of the accurate sideband 
calibration is to model the
atmosphere properly. It has to be an iterative process: atmospheric 
modeling is required
to derive the gain ratio, but the gain ratio is required in atmospheric 
modeling.

Besides relatively narrow interstellar lines like CO in absorption against 
quasars, the Ozone
lines near 219 GHz (if my memory is right) have been clearly seen at 
Plateau de Bure to affect
the bandshape. Modelling these lines is mandatory.


         Good luck

         Stephane