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SUBROUTINE sla_FK54Z (R2000,D2000,BEPOCH,
: R1950,D1950,DR1950,DD1950)
*+
* - - - - - -
* F K 5 4 Z
* - - - - - -
*
* 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 sla_FK524 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: sla_FK524, sla_PM
*
* P.T.Wallace Starlink 10 April 1990
*
* Copyright (C) 1995 Rutherford Appleton Laboratory
*-
IMPLICIT NONE
DOUBLE PRECISION R2000,D2000,BEPOCH,
: R1950,D1950,DR1950,DD1950
DOUBLE PRECISION R,D,PX,RV
* FK5 equinox J2000 (any epoch) to FK4 equinox B1950 epoch B1950
CALL sla_FK524(R2000,D2000,0D0,0D0,0D0,0D0,
: R,D,DR1950,DD1950,PX,RV)
* Fictitious proper motion to epoch BEPOCH
CALL sla_PM(R,D,DR1950,DD1950,0D0,0D0,1950D0,BEPOCH,
: R1950,D1950)
END
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