[daip] Re: CLCOR position shifts (fwd)

[Leonia Kogan]

Mark,

Andreas wrote:

>It could also be that the initial apparent positions in the SU table are 
>wrong and CLCOR calculates in the first shift the J2000 of this wrong 
>coordinates.

I think this one of the posible solution of the problem.  Andreas can
run CLCOR with the opposite sign of the correction and see if the both
aparent and epoch coordinates will return back to the origional ones.

Can Andreas look at the SCHED output and see the both right coordinates there?

2. I hope he followed the HELP file to uce correctely the COS(delta)
   for the RA correction

Leonia 
----- Begin Included Message -----

>From reid at cfa.harvard.edu Wed Sep  4 07:44 MDT 2002
Date: Wed, 4 Sep 2002 09:43:54 -0400 (EDT)
From: Mark Reid <reid at cfa.harvard.edu>
X-X-Sender: reid at mjr.harvard.edu
To: lkogan at cv3.cv.nrao.edu
cc: lgreenhill at cfa.harvard.edu
Subject: Re: CLCOR position shifts (fwd)
MIME-Version: 1.0
X-MailScanner: Found to be clean
X-Lines: 62
Status: RO


Leonia,

I got this message from Andreas Brunthaler.
Apparently, even with the very awkward convention
of shifting in apparent coordinates (when everything
else is done in J2000 coordinates), there still are
serious errors in the SU table.

Mark


-------------------------------------------------------------
Mark J. Reid                 Phone: 617-495-7470 
Harvard-Smithsonian CfA      Fax  : 617-495-7345
60 Garden Street             Email: reid at cfa.harvard.edu
Cambridge, MA 02138, USA     Web  : cfa-www.harvard.edu/~reid                  
-------------------------------------------------------------


---------- Forwarded message ----------
Date: Wed, 04 Sep 2002 13:55:01 +0200
From: Andreas Brunthaler <brunthal at mpifr-bonn.mpg.de>
To: Mark Reid <reid at cfa.harvard.edu>
Subject: Re: CLCOR position shifts (fwd)

Mark,

the J2000 coordinates get also updated, but not as they should. 
These are the coordinates i get in the SU table before and after a 
shift of -0.00409 arcsec in DEC:

before shift:

      RAEPO	     DECEPO	  |	RAAPP           DECAPP
6.7636903750E+00 5.9981378722E+01 | 6.7661974065E+00 5.9985040301E+01

after shift:

      RAEPO	     DECEPO	  |	 RAAPP          DECAPP
6.7637355776E+00 5.9981300756E+01 | 6.7661974065E+00 5.9985039165E+01

The DECAPP got changed correctly by -0.00409 arcsec. However, the DECEPO 
changed by -0.2806776 arcsec, and the RAEPO by 0.1627296 arcsec. So the 
J2000 coordinates changed in total by more than 0.32 arcseconds after a 
shift of only 0.00409 arcseconds.

If I apply a SECOND or third shift, it changes all coordinates by the 
right amount. The first shift is always wrong by this 0.32 arcsec.

Kogan wrote that the new J2000 coordinates are calculated from the the 
new apparent positions. It seems that there is an offset of 0.32 arcsec 
in this conversion. The first shift then calculates a wrong J2000 position.
It could also be that the initial apparent positions in the SU table are 
wrong and CLCOR calculates in the first shift the J2000 of this wrong 
coordinates.

Andreas






----- End Included Message -----