.help fk54z Jun99 "Slalib Package"
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      SUBROUTINE slF54Z (R2000,D2000,BEPOCH,
     :                      R1950,D1950,DR1950,DD1950)

     - - - - - -
      F 5 4 Z
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  Convert a J2000.0 FK5 star position to B1950.0 FK4 assuming
  zero proper motion and parallax (double precision)

  This routine converts star positions from the new, IAU 1976,
  FK5, Fricke system to the old, Bessel-Newcomb, FK4 system.

  Given:
     R2000,D2000     dp    J2000.0 FK5 RA,Dec (rad)
     BEPOCH          dp    Besselian epoch (e.g. 1950D0)

  Returned:
     R1950,D1950     dp    B1950.0 FK4 RA,Dec (rad) at epoch BEPOCH
     DR1950,DD1950   dp    B1950.0 FK4 proper motions (rad/trop.yr)

  Notes:

  1)  The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt.

  2)  Conversion from Julian epoch 2000.0 to Besselian epoch 1950.0
      only is provided for.  Conversions involving other epochs will
      require use of the appropriate precession routines before and
      after this routine is called.

  3)  Unlike in the slFK54 routine, the FK5 proper motions, the
      parallax and the radial velocity are presumed zero.

  4)  It is the intention that FK5 should be a close approximation
      to an inertial frame, so that distant objects have zero proper
      motion;  such objects have (in general) non-zero proper motion
      in FK4, and this routine returns those fictitious proper
      motions.

  5)  The position returned by this routine is in the B1950
      reference frame but at Besselian epoch BEPOCH.  For
      comparison with catalogues the BEPOCH argument will
      frequently be 1950D0.

  Called:  slFK54, slPM

  P.T.Wallace   Starlink   10 April 1990

  Copyright (C) 1995 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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