[fitsbits] Fits Table Entries Referring to Keywords

[Bill Cotton]

Randall Smith writes:
 > 
 > I've been writing a X-ray spectral calculation code (given a
 > temperature between 10^4 and 10^9 K, and a (low) density, calculate
 > the emitted spectrum), and storing all the requisite atomic data in
 > FITS files (website at http://hea-www.harvard.edu/APEC).  
 > 
 > I'd like to give detailed references to all of the atomic data, on a
 > rate-by-rate basis.  The data is stored in FITS binary tables, with a
 > 40 character ASCII column for references.  This is enough to give a
 > reference for that data that can be reasonably easily parsed by a
 > human.  What I'd like to do is change this to store the complete,
 > journal-quality references in the header and then give a lookup value
 > in the file.  Ie, on a particular line give the reference as "ZS87",
 > and then in the header somehow list 
 > ZS87 = "Zhang,~H \& Sampson,~D.  1987, ApJ, 581, 183"
 > 
 > What I'm wondering is, is there any kind of standard for this?  I could
 > make the ZS87 a keyword with a long string value equal to the full
 > reference.  However, I'd like to have complete freedom in making up
 > the lookup value, and that means there could be a conflict between the
 > lookup value keyword and a real, well-defined FITS keyword.   Or I 
 > could use COMMENT statements which I could then parse, but this
 > information is an important part of the file, and relegating it to
 > "COMMENT" status doesn't seem right either.
 > 
 > Any suggestions?
 > 

   One possibility is to have another table with two columns, one for
the reference code and one for the full reference.  Since this table
would be relatively small(?) a large, fixed allocation (200 bytes?)
for the full reference would be reasonable.  If size is a problem,
variable length strings could be used.  This has the advantage over
keywords that conflicts with other keyword names and the restrictions
on FITS keywords are avoided.  This table could also be reused in your
next release.  
   What about a column for URLs of online papers?

Bill Cotton
NRAO