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Antoine Couette wrote:
> To help me here, just be so kind as to indicate to me which Precession 
> data set you are currently using in your software (I would be guessing 
> that you might be using our current (is it 2002 ? or rather 2004 ?) IAU 
> recommended values.

In 2006 the IAU recommended a new precession / nutation model, to go
into effect in 2009:
http://www.iau.org/static/resolutions/IAU2006_Resol1.pdf

I use the SOFA implementation:
http://www.iausofa.org/2009_0201_F/sofa/pnm06a.html

It generates a rotation matrix to convert a vector from the GCRS to the
true equator and equinox of date, with IAU 2006 precession / nutation.


Coordinates of kappa Cancri at your immersion time:

1901-03-02T22:43:32.30 Terrestrial Time
1901-03-02T22:43:33.40 UT1
-1.10 delta T (TT-UT1)

observer position
+48°23'30.0" -  4°29'31.2"  N lat, E lon
0 m (0 ft) above ellipsoid

kappa Cancri = name of body

Barycentric right ascension and declination in the ICRS. These are the
ICRS coordinates at the occultation time. I.e., they are the Hipparcos
catalog coordinates adjusted for proper motion. At .1" accuracy, there
is no significant difference between the ICRS (or GCRS) and the J2000
mean equator and equinox.
  9h07m44.95s +10°40'06.5"  RA, dec

Geocentric apparent coordinates in the GCRS. These are the above
coordinates plus aberration. Parallax is insignificant for this star.
  9h07m46.13s +10°40'00.2"  RA, dec

Geocentric apparent coordinates with respect to the true equator and
equinox at the occultation time. These are the above coords, plus IAU
2006 precession / nutation.
  9h02m25.79s +11°03'44.2"  RA (equinox), dec

Unrefracted topocentric coordinates. These are the above coordinates
plus dinural aberration, and converted to the observer's horizontal
coordinate system.
181°18'44.6"  52°39'52.0"  37°20'08.0"  az, el, ZD


Here are values from the USNO MICA 2.0 program.

geocentric apparent (true equator of date)
  9h02m25.771s +11°03'44.30"  RA, dec

unrefracted topocentric
181°18'44.7" 37°20'07.9"  az, zenith distance

MICA uses the IAU 1976 precession and 1980 nutation.

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