[daip] VLA A-array FITS and ps files - AL218 Snapshot Survey (Texas Survey Sources) (fwd)

[Ray Lucas]

Hi,

Your email address was suggested to me as a place to ask some of these
questions.

I'm providing some reduced VLA A-array 20cm 1485MHz snapshots from
~1990 to the MAST Archive at STScI, and they had these comments on
the FITS header keywords, and they wondered a bit about the data
structures. I'm not so sure what to ask you about the latter, and
unless they say they have some problem with what I'm providing them
(they're just going to look into it), I guess I'm less concerned
about that at the moment. But if there is no problem with making
the changes they request with regard to the header keywords, I
plan to make those changes soon.

I would guess that since they are asking me to make these changes,
these things should be understood well enough so that they will
not pose any problem for most users, but I just wanted to run this
past you as well since this is radio data and you will likely know
better than anyone else if there will be any bad side effects from
this for people who usually use AIPS etc. instead of other software
like iraf/stsdas, etc. (Since many people using this multiple mission
archive (MAST) data will be using optical/uv/ir astronomy tools, and
that radio astronomers also use those same tools in addition to AIPS,
I imagine that these changes will probably pose no problems for anyone,
but just wanted to run it by you as well.)

See comments from STScI MAST folks below.

Thanks,
Ray Lucas

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1) the deprecated EPOCH keyword is used (EQUINOX is now recommended)

2) the deprecated BLOCKED keyword is used. This was originally used to
describe tape files where more than one logical record was contained
within one tape record. As far as I know it has no meaning for disk FITS
files but its use is not recommended.

3) Less important, the BSCALE and BZERO keywords are legally specified
but they serve no purpose. Including them will just mean that every data
point will be multiplied by 1.0 and 0.00 added. They were originally used
so floating point numbers could be specified using scaled integers.

In order to archive your files, I would suggest to change the EPOCH
keyword to EQUINOX and remove the BLOCKED keyword. The BSCALE and BZERO
are an unnecessary complication, but they won't do any harm. So, if you
don't want to remove them, that's fine as well. Do you think you could do
these changes?

I was trying to understand the data structure. Your fits files contain
(1024x1024x1x1) arrays. I am used to having all the frequencies in one
large datacube. It seems that these files contain only one frequency each.
I guess, I should better have a look at your AAS file and the attached
paper. I'll do that this week.

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