| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | void slaFk54z ( double r2000, double d2000, double bepoch,
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| 4 | double *r1950, double *d1950,
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| 5 | double *dr1950, double *dd1950 )
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| 6 | /*
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| 7 | ** - - - - - - - - -
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| 8 | ** s l a F k 5 4 z
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| 9 | ** - - - - - - - - -
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| 10 | **
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| 11 | ** Convert a J2000.0 FK5 star position to B1950.0 FK4 assuming
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| 12 | ** zero proper motion and parallax.
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| 13 | **
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| 14 | ** (double precision)
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| 15 | **
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| 16 | ** This routine converts star positions from the new, IAU 1976,
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| 17 | ** FK5, Fricke system to the old, Bessel-Newcomb, FK4 system.
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| 18 | **
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| 19 | ** Given:
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| 20 | ** r2000,d2000 double J2000.0 FK5 RA,Dec (rad)
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| 21 | ** bepoch double Besselian epoch (e.g. 1950)
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| 22 | **
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| 23 | ** Returned:
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| 24 | ** *r1950,*d1950 double B1950.0 FK4 RA,Dec (rad) at epoch BEPOCH
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| 25 | ** *dr1950,*dd1950 double B1950.0 FK4 proper motions (rad/trop.yr)
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| 26 | **
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| 27 | ** Notes:
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| 28 | **
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| 29 | ** 1) The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt.
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| 30 | **
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| 31 | ** 2) Conversion from Julian epoch 2000.0 to Besselian epoch 1950.0
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| 32 | ** only is provided for. Conversions involving other epochs will
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| 33 | ** require use of the appropriate precession routines before and
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| 34 | ** after this routine is called.
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| 35 | **
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| 36 | ** 3) Unlike in the slaFK524 routine, the FK5 proper motions, the
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| 37 | ** parallax and the radial velocity are presumed zero.
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| 38 | **
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| 39 | ** 4) It is the intention that FK5 should be a close approximation
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| 40 | ** to an inertial frame, so that distant objects have zero proper
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| 41 | ** motion; such objects have (in general) non-zero proper motion
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| 42 | ** in FK4, and this routine returns those fictitious proper
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| 43 | ** motions.
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| 44 | **
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| 45 | ** 5) The position returned by this routine is in the B1950
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| 46 | ** reference frame but at Besselian epoch bepoch. For
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| 47 | ** comparison with catalogues the bepoch argument will
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| 48 | ** frequently be 1950.0.
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| 49 | **
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| 50 | ** Called: slaFk524, slaPm
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| 51 | **
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| 52 | ** Last revision: 30 October 1993
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| 53 | **
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| 54 | ** Copyright P.T.Wallace. All rights reserved.
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| 55 | */
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| 56 | {
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| 57 | static double zero = 0.0;
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| 58 |
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| 59 | double r, d, px, rv;
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| 60 |
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| 61 | /* FK5 equinox J2000 (any epoch) to FK4 equinox B1950 epoch B1950 */
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| 62 | slaFk524 ( r2000, d2000, zero, zero, zero, zero,
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| 63 | &r, &d, dr1950, dd1950, &px, &rv );
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| 64 |
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| 65 | /* Fictitious proper motion to epoch bepoch */
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| 66 | slaPm ( r, d, *dr1950, *dd1950, zero, zero, 1950.0, bepoch,
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| 67 | r1950, d1950 );
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| 68 | }
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