slaAmpqk -

SYNOPSYS

PARAMETERS

double ra

double da

double *amprms

double *rm

double *dm

DESCRIPTION

  Convert star RA,Dec from geocentric apparent to mean place.

  The mean coordinate system is the post IAU 1976 system,
  loosely called FK5.

  Use of this routine is appropriate when efficiency is important
  and where many star positions are all to be transformed for
  one epoch and equinox.  The star-independent parameters can be
  obtained by calling the slaMappa routine.

Given

     ra       double      apparent RA (radians)
     da       double      apparent Dec (radians)

       (0)      time interval for proper motion (Julian years)
       (1-3)    barycentric position of the Earth (AU)
       (4-6)    heliocentric direction of the Earth (unit vector)
       (7)      (grav rad Sun)*2/(Sun-Earth distance)
       (8-10)   abv: barycentric Earth velocity in units of c
       (11)     sqrt(1-v*v) where v=modulus(abv)
       (12-20)  precession/nutation (3,3) matrix

Returned

     *rm      double      mean RA (radians)
     *dm      double      mean Dec (radians)

References

     1984 Astronomical Almanac, pp B39-B41.
     (also Lederle & Schwan, Astron. Astrophys. 134, 1-6, 1984)

Notes

  1)  The accuracy is limited by the routine slaEvp, called
      by slaMappa, which computes the Earth position and
      velocity using the methods of Stumpff.  The maximum
      error is about 0.3 milliarcsecond.

  2)  Iterative techniques are used for the aberration and
      light deflection corrections so that the routines
      slaAmp (or slaAmpqk) and slaMap (or slaMapqk) are
      accurate inverses;  even at the edge of the Sun's disc
      the discrepancy is only about 1 nanoarcsecond.

Called

 slaDcs2c, slaDimxv, slaDvdv, slaDvn, slaDcc2s,
           slaDranrm

  P.T.Wallace   Starlink   31 October 1993

SEE ALSO

• slalib.3