[daip] Re: CLCOR position shifts (fwd)

[Andreas Brunthaler]

Leonia Kogan wrote:
> 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.

I tried a shift with the opposite sign, and the apparent coordinates 
return to their original values. The epoch coordinates don't.

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

The J2000 coordinates are the same in the SCHED output and the SU-Table. 
The apparent coordinates are different from the SU-Table.

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

As Mark mentioned, I applied a DEC-shift only.


Andreas


> 
> 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
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> 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 -----
> 
>