[Almasci] Re: [mmaimcal]Re: Comment in ALMA memo 489

[Stephane Guilloteau]

A couple of side points which may help improving the algorithm(s) or our understanding of these algorithms

1) CLEAN with or without the zero spacing is not the same
        - because we add an offset into the map, the positive and negative components are different. So CLEAN
converges toward a quite different solution as soon as (non null) zero-spacing flux is added. The zero spacing flux,
despite the fact it is not "localized" helps solving for other scales in the image !
        - the above point is perhaps obvious to most of us, but in the discussion, I had the impression the non-linear
nature of CLEAN was lost.

2) So far, there is no way to tell CLEAN where to locate the extended emission
     - yet, we A PRIORI KNOW this extended emission is not entirely flat: there is the primary beam which attenuates the
sky brightness...

    Has anybody an idea on how to incoporate that "a priori" information into CLEAN ?
    Perhaps  let the final "missing" flux be localized just as the (primary) beam ? At least, that would look a better
guess...

        Stephane