[daip] help with AIPS

[Amy Mioduszewski]

Eric is away for a couple weeks, I will try to answer your questions.

Melanie Gendre wrote:
> Hi,
> 
> I have been in communication with Eric Greisen about some issues I have
> with AIPS, but I am still nowhere near understanding what's going on, and
> I can't seem to get anything from the Cookbook.
> 
> Here's the situation:
> I have VLA data at 90cm taken in BnA and CnB configurations, covering a 6
> deg^2 field in 2 pointings (I have therefore 4 uv data files when I do
> SPLIT).
> I did the calibration of the data using the standard procedure FILLM,
> LISTR, QUACK, SETJY, CALIB, EDITA, GETJY, EXTDEST, CLCAL, SNPLT, SPLIT,
> UVSRT.
> 
> The difference between these data and what I usually do is that I have
> several sources for each uv file (each pointings) and I'd like to get flux
> and contour plots for each sources individually.
> 
> Eric suggested that I:
> - use SETFC to get the recommended CELLSIZE
> - change the CELLSIZE to a rounder close number and re-run SETFC to write
> the boxfile
> - use FLATN to make one large image of all the facets
> - use SAD or JMFIT to get the flux
> 
> My (numerous) issues are:
> (1) What are the differences between "pointings", "sources", "fields" and
> "facets" in the AIPS jargon? I am confused between all those terms. If I
> have several sources in one pointing, does that mean I have one field or
> several fields?
A pointing is where the telescope was pointing, so it sounds like you have 2 
pointings.  Sources are sources.  Fields is harder, he probably means the same 
things as facets, because you set "fields" in IMAGR, which are the individual 
areas to image.

What SETFC does is split the area you observed into smaller areas for wide-field 
3D imaging.  IMAGR assumes that the sky is flat and since it obviously isn't you 
need to break a large area into smaller areas.  You can run SETFC so it will 
create fields around sources found in the NVSS or WENSS surveys as well (see 
EXPLAIN SETFC).  But if you don't do this then it just breaks the area up 
regardless of if you have a source or sources in the field.

> (2) Why do I have to run SETFC twice?
You don't *have* to run SETFC twice, it is just it usually picks a cell size 
that is not aesthetically pleasing (for the lack of a better description), like 
2.1028469264asec when it would just be more pleasant to have a cell size of 
something like 2asec.

> (3) What exactly does the BOXFILE do? Does it isolate my sources?

BOXFILE from SETFC defines the fields to be imaged.  BOXFILEs can also have 
clean boxes defined in them, but SETFC does not do this.

> (4) When I follow the procedure with SETFC, the output boxfile is empty.
> Why? (My guess would be that it's because nowhere do I tell AIPS there
> should be several boxes)

Does SETFC run without error?  Send me your inputs.  SETFC should figures out on 
its own how many boxes (fields) you need.  Maybe you don't need more than one 
field.

> (5) I actually know where the sources should be (I have the list of
> coordinates). Could that help in the reduction? If so, how?
> I tried to input this list of sources in INFILE in SETFC, and I get a
> BOXFILE output, but I am not sure of how reliable it is.

Yes, you should be able to get SETFC to make fields around your sources.  How 
reliable what is?  Do you use the correct format for your list?

> (6) Which leads to the question: how do I isolate my sources?

I don't know what you are asking.  Isolate in what way?  Clean them?  If you 
want to set clean boxes, you box them in IMAGR.

> (7) In JMFIT, how do you point to each source individually? I can't see
> any input coordinate/file
> 

You box them with TVWIN, (ie, fill in BLC, TRC), JMFIT needs to fit an area not 
just a coordinate.

> 
> Maybe getting some insight of what the procedure is when you don't know
> what sources you have in the image would help me understand how this all
> works. I am getting really confused and a bit frustrated, and I'm sure
> it's just because I'm missing (or misunderstanding) something small...

Well it sounds like SETFC didn't give you what you wanted.  Once you get the 
fields set up it should be pretty easy.  Is there anyone there that can help you 
run IMAGR?

Good luck!

Amy