[daip] CLCOR SU table update problem (?)

[Lincoln Greenhill]

Hi Eric,

> I have not followed the previous exchange, but have a question.  Where
> did the initial pairing of J2000 and apparent coordinates came from?
> If it was a FITLD prior to the recent corrections then that pair a not
> a correct match - being wrong by about a day due to FITLD.  Any use of
> such a pair thereafter, with code that does not make the ~1 day error,
> will cause just what you describe.

Thank you for spurring me to look into this.

Are you referring to the entry 10928 of CHANGE.DOC (setting DELDAT=1e-06)
or to entry 10798 (FPARSE for equinox)?

I presume you refer to the former. The data was loaded at the AOC with
31DEC01 FITLD in mid-late June '01, and it is therefore afflicted with 
erroneous apparent coordinates (change #10928).

Using v. recently loaded data, I have checked that the change in
J2000 coordinates sparked by CLCOR is the right order of magnitude.
All is well, almost.

My precision precession/nutation software predicts a modified J2000
coordinate that still does not agree with that CLCOR-modified J2000
coordinate.  The difference is on the order of 5 mas, and for a source at
the equator, I believe my software is good at the 1 mas level.  I
may have identified the cause...I notice that the GR correction in JPREC
is turned off (GR=.FALSE).  Why?


Regards,

Lincoln


Lincoln J. Greenhill      Harvard-Smithsonian Center for Astrophysics 
Radio & Geoastronomy Division, 60 Garden St, Cambridge, MA 02138, USA
Telephone:  1 617-495-7194             FAX:  1 617-495-7345
Internet:  greenhill at cfa.harvard.edu   http://cfa-www.harvard.edu/~lincoln