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.
r2000,d2000 double J2000.0 FK5 RA,Dec (rad) bepoch double Besselian epoch (e.g. 1950)
*r1950,*d1950 double B1950.0 FK4 RA,Dec (rad) at epoch BEPOCH *dr1950,*dd1950 double B1950.0 FK4 proper motions (rad/trop.yr)
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 slaFK524 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 1950.0.
slaFk524, slaPm P.T.Wallace Starlink 30 October 1993