[daip] CLCOR precession/nutation

Mon Sep 16 12:29:17 EDT 2002

Lincoln,

Craig Walker has returned back from the short vacation. So I had a chance to 
ask him about the time for the aparent coordinates in SCHED.

His answer is: "the stop of the first scan"

The stop of the first scan of the observation, I choose accidentely
is very close to half day (11:57:21)

Inside of the CLCOR/FITLD the subroutine JULDAY(OBSDAT, JD) calculates the 
JD for OBSDAT='20020811', JD = 2452497.5.
 At the JULDAY language, SCHED calculates the aparent coordinates 
for the time which is 0.5day(stop of the first scan) later than the 'OBSDAT'

So JD =2452498.0

I reported in my previous message that the AIPS task JPRECS gives 
the apparent coordinates which are in the good agreement with SCHED 
(error <1mas), if the JD of SCHED is equal 2452498.0

Now I see that 2452498.0 is the right choice for JD (inside of CLCOR) 
to compare with SCHED for the chosen observation.

The conclussion: JPRECS' apparent coordinates coincide with SCHEd's ones 
with error <1mas.

Please pay attention that JPRECS takes care about abberatin and the relativic 
bind of the ray because of the SUN (not only precession and nutation.

Leonia

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>From daip-admin at donar.cv.nrao.edu Tue Sep 10 09:57 MDT 2002
From: Leonia Kogan <lkogan at aoc.nrao.edu>
To: lincoln at play.harvard.edu
Cc: daip at cv3.cv.nrao.edu, brunthal at mpifr-bonn.mpg.de, reid at cfa.harvard.edu
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Subject: [daip] CLCOR  precession/nutation
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Date: Tue, 10 Sep 2002 09:55:49 -0600 (MDT)
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Lincoln,

The following table is the result of my test.

I took one of the current VLBA observations correlated at our correlator 
recentely.

The source is 0420-014  RAEPO = 65.815836363; DECEPO = -1.3425181417 (degrees)
time of observation is '20020811'
Julian day as it seen at CLCOR (output of JULDAY) is 2452497.5
SCHED as I know uses the even number for JD
I run CLCOR with the modification included JPRECS (dir=1) to calculate the
apparent coordinates (it is done actually in FITLD.
The table includes JD=2452497.5, 2452497.0, and 2452498 for CLCOR
and SCHED JD=?  

                |      RAAPP       |     DECAPP       | 
------------------------------------------------------|
SCHED JD=?      |  65.843370058    |    -1.334762314  |

JPRECS 
JD=2452497.5    |  65.843321304    |    -1.334782473  |
JD=2452497.0    |  65.843270279    |    -1.334805072  |
JD=2452498.0    |  65.843370075    |    -1.334762001  |
-------------------------------------------------------

If sched uses JD=2452498.0, then

deltaRA= 2.0E-8degrees=0.072mas;  deltaDEC= 3.0e-7degrees=1mas

Craig Walker is the only one who can answer the question about 
JD in SCHED. I can not find him right now.

JPRECS was ran with OPSPOS at the Earth center(no duarnal abberation)
and with POLAR=0.

I hope you can carry out your own test

Cheers

Leonia
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>From lincoln at play.harvard.edu Mon Sep  9 16:00 MDT 2002
Date: Mon, 9 Sep 2002 18:00:25 -0400 (EDT)
From: Lincoln Greenhill <lincoln at play.harvard.edu>
To: lkogan at cv3.cv.nrao.edu
cc: brunthal at mpifr-bonn.mpg.de, <reid at cfa.harvard.edu>,
        <aipsmail at cv3.cv.nrao.edu>
Subject: CLCOR  precession/nutation
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Hi Leonia,

I am a bit distressed to learn of the problem that
you have been discussion with Andreas Brunthaler and that
has existed in AIPS for that last > 9 months.

You and I have had some discussions relating to my testing
the AIPS routines against my own, which should have milliarcsec
precision but have not demonstrated agreement with AIPS at
levels of 5 to 20 mas.

I note the followng email that I sent last year:

-------------------------------------------

>From daip-admin at donar.cv.nrao.edu Wed Oct 10 08:36 MDT 2001
From: Lincoln Greenhill <lincoln at play.harvard.edu>
To: Leonia Kogan <lkogan at zia.aoc.NRAO.EDU>
Subject: Re: [daip] CLCOR  SU table update  problem (?)

Hi Leonia,

In FITLD, JPRECS is run w/o GR.
Perhaps this code, which is part
of an if-then is not called?

I am concerned about the 5 mas discrepancy
between my precession/nutation code and AIPS' code.
Perhaps I jumped to conclusions as to what might be
responsible for the discrepancy.

How accurate is JPREC supposed to be?

------------------------------------------

I would again like to make a test of AIPS and to compare it to my
routines.  To make this as easy as possible, I would appreciate it
if you would create a v. short FITS file using corrected AIPS and
tell me what time to use for the precession and nutation.  I'll ftp
the file from NRAO.  By using your data file, I can be absolutely
sure of consistency, which was difficult to achieve last year.

I'd also like to reinforce a comment that Mark made earlier.
It does not make sense to me that shifts in CLCOR are in apparent
sky coordinates, given that all maps and UV coordinates are in
the J2000 frame.

Regards,

Lincoln

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