Re: Common and uncommon goals and software

[Jure Skvarc <jure.skvarc@ijs.si>]

Michael G. proposed a minimal set of data for each star which should be present
in FITS tables.  I have some remarks:

x and y coordinates are nice to have but I don't think they belong to the
minimum set of data needed for further work.  I see no need to carry the Julian
Day together with each star.  This datum belongs to the FITS header because it
is the same for all objects.  Anybody capable of putting the FITS table contents
into some database will read the JD and add it to the record.  

I suspect that fwhm[xy] are not well defined quantities and not very useful,
too. Variation of star shapes across the field is quite large due to coma. Star
shapes can not be assumed to have major and minor axis in x and y directions.  
It would be more informative to have a formally computed positional error
estimate based on centroiding and catalog uncertainties.  However, these
quantities in my opinion also do not belong to the minimal set of data.

One thing that might be useful is the airmass.  This would normally be in the
header but the field of view is so big that it maybe makes a difference.

So:

Header (obligatory)
JD  Julian Day
FILTER
EXPOSURE exposure time
DATE-OBS start of observing (date + time)
OBSERVER observatory code or information how to get observatory coordinates

Table (obligatory)
RA
DEC
MAG
MAGERR
AIRMASS

Table (optional)
XT, YT image coordinates
SXT, SYT error estimates
SRA, SDEC error estimates for ra, dec
CATALOG  if the star is identified, catalog name
CATID     star id, if it is identified
:
:         maybe more
:




				regards, Jure


 
> The FITS header would be a copy from the raw file with the exception of the
> image data itself.
> 
> The star list itself would include the following fields:
> 
> * x
> * y
> * ra
> * dec
> * mag
> * mag error
> * fwhmx
> * fwhmy
> * julian date
> 
> Comments?
> 
>