SUBROUTINE iau_FK54Z ( R2000, D2000, BEPOCH, : R1950, D1950, DR1950, DD1950 ) *+ * - - - - - - - - - - * i a u _ F K 5 4 Z * - - - - - - - - - - * * Convert a J2000.0 FK5 star position to B1950.0 FK4, assuming zero * proper motion in FK5 and parallax. * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: support routine. * * Given: * R2000,D2000 d J2000.0 FK5 RA,Dec (rad) * BEPOCH d Besselian epoch (e.g. 1950D0) * * Returned: * R1950,D1950 d B1950.0 FK4 RA,Dec (rad) at epoch BEPOCH * DR1950,DD1950 d B1950.0 FK4 proper motions (rad/trop.yr) * * Notes: * * 1) In contrast to the iau_FK524 routine, here the FK5 proper motions, * the parallax and the radial velocity are presumed zero. * * 2) This routine converts a star position from the IAU 1976 FK5 * (Fricke) system to the former FK4 (Bessel-Newcomb) system, for * cases such as distant radio sources where it is presumed there is * zero parallax and no proper motion. Because of the E-terms of * aberration, such objects have (in general) non-zero proper motion * in FK4, and the present routine returns those fictitious proper * motions. * * 3) Conversion from J2000.0 FK5 to B1950.0 FK4 only is provided for. * Conversions involving other equinoxes would require additional * treatment for precession. * * 4) The position returned by this routine is in the B1950.0 FK4 * reference system but at Besselian epoch BEPOCH. For comparison * with catalogs the BEPOCH argument will frequently be 1950D0. (In * this context the distinction between Besselian and Julian epoch is * insignificant.) * * 5) The RA component of the returned (fictitious) proper motion is * dRA/dt rather than cos(Dec)*dRA/dt. * * Called: * iau_ANP normalize angle into range 0 to 2pi * iau_C2S p-vector to spherical * iau_FK524 FK4 to FK5 * iau_S2C spherical to p-vector * * This revision: 2023 March 5 * * SOFA release 2023-10-11 * * Copyright (C) 2023 IAU SOFA Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION R2000, D2000, BEPOCH, : R1950, D1950, DR1950, DD1950 DOUBLE PRECISION R, D, PR, PD, PX, RV, P(3), W, V(3) INTEGER I DOUBLE PRECISION iau_ANP * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * FK5 equinox J2000.0 to FK4 equinox B1950.0. CALL iau_FK524 ( R2000, D2000, 0D0, 0D0, 0D0, 0D0, : R, D, PR, PD, PX, RV ) * Spherical to Cartesian. CALL iau_S2C ( R, D, P ) * Fictitious proper motion (radians per year). V(1) = - PR*P(2) - PD*COS(R)*SIN(D) V(2) = PR*P(1) - PD*SIN(R)*SIN(D) V(3) = PD*COS(D) * Apply the motion. W = BEPOCH - 1950D0 DO 1 I=1,3 P(I) = P(I) + W*V(I) 1 CONTINUE * Cartesian to spherical. CALL iau_C2S ( P, W, D1950 ) R1950 = iau_ANP ( W ) * Fictitious proper motion. DR1950 = PR DD1950 = PD * Finished. *+---------------------------------------------------------------------- * * Copyright (C) 2023 * Standards of Fundamental Astronomy Board * of the International Astronomical Union. * * ===================== * SOFA Software License * ===================== * * NOTICE TO USER: * * BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND * CONDITIONS WHICH APPLY TO ITS USE. * * 1. The Software is owned by the IAU SOFA Board ("SOFA"). * * 2. Permission is granted to anyone to use the SOFA software for any * purpose, including commercial applications, free of charge and * without payment of royalties, subject to the conditions and * restrictions listed below. * * 3. You (the user) may copy and distribute SOFA source code to others, * and use and adapt its code and algorithms in your own software, * on a world-wide, royalty-free basis. 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The provision of any version of the SOFA software under the terms * and conditions specified herein does not imply that future * versions will also be made available under the same terms and * conditions. * * In any published work or commercial product which uses the SOFA * software directly, acknowledgement (see www.iausofa.org) is * appreciated. * * Correspondence concerning SOFA software should be addressed as * follows: * * By email: sofa@ukho.gov.uk * By post: IAU SOFA Center * HM Nautical Almanac Office * UK Hydrographic Office * Admiralty Way, Taunton * Somerset, TA1 2DN * United Kingdom * *----------------------------------------------------------------------- END