[mmaimcal]Re: Comment in ALMA memo 489

[Michael Rupen]

Hello all,
  a quick response to one of Stephane's points --

> Mark also says a guard band in Single-Dish mode ONLY also improves the 
> image quality. If I have followed correctly the discussion, I believe 
> the only demonstration of that (if any) is based on data where there was 
> NO EMISSION outside the mosaicked area. May be I am mistaken, but in 
> case this is true, I believe it is important to check whether a guard band
> also helps when the source is more extended than the mosaicked area, 
> because this is likely to be the actual situation.

I've done this in practice, if not in theory, in several cases, and the
guard band does seem to help, mainly in modeling the extended structure
(errors in which tend to dominate current maps).  This is VLA + 140-foot
HI stuff.  Others must have similar experience, since it's so much more 
expensive to get interferometric observations, and basically trivial to 
get a little extra single-dish time to observe the guard band; and as 
Stephane says emission extending beyond the area of interest is likely to 
be the rule when mosaicking, rather than the exception.  Does 
this match other people's current experience?  Of course this may not be 
relevant to the infinitely better data ALMA will produce.

Cheers,

       Michael Rupen
       NRAO/Socorro