| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | void slaFk5hz ( double r5, double d5, double epoch, double *rh, double *dh )
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| 4 | /*
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| 5 | ** - - - - - - - - -
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| 6 | ** s l a F k 5 h z
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| 7 | ** - - - - - - - - -
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| 8 | **
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| 9 | ** Transform an FK5 (J2000) star position into the frame of the
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| 10 | ** Hipparcos catalogue, assuming zero Hipparcos proper motion.
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| 11 | **
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| 12 | ** (double precision)
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| 13 | **
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| 14 | ** This routine converts a star position from the FK5 system to
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| 15 | ** the Hipparcos system, in such a way that the Hipparcos proper
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| 16 | ** motion is zero. Because such a star has, in general, a non-zero
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| 17 | ** proper motion in the FK5 system, the routine requires the epoch
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| 18 | ** at which the position in the FK5 system was determined.
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| 19 | **
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| 20 | ** Given:
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| 21 | ** r5 double FK5 RA (radians), equinox J2000, epoch EPOCH
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| 22 | ** d5 double FK5 Dec (radians), equinox J2000, epoch EPOCH
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| 23 | ** epoch double Julian epoch (TDB)
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| 24 | **
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| 25 | ** Returned (all Hipparcos):
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| 26 | ** rh double RA (radians)
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| 27 | ** dh double Dec (radians)
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| 28 | **
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| 29 | ** Called: slaDcs2c, slaDav2m, slaDimxv, slaDmxv, slaDcc2s, slaDranrm
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| 30 | **
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| 31 | ** Notes:
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| 32 | **
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| 33 | ** 1) The FK5 to Hipparcos transformation consists of a pure
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| 34 | ** rotation and spin; zonal errors in the FK5 catalogue are
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| 35 | ** not taken into account.
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| 36 | **
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| 37 | ** 2) The published orientation and spin components are interpreted
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| 38 | ** as "axial vectors". An axial vector points at the pole of the
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| 39 | ** rotation and its length is the amount of rotation in radians.
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| 40 | **
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| 41 | ** 3) See also slaFk52h, slaH2fk5, slaHfk5z.
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| 42 | **
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| 43 | ** Reference:
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| 44 | **
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| 45 | ** M.Feissel & F.Mignard, Astron. Astrophys. 331, L33-L36 (1998).
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| 46 | **
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| 47 | ** Last revision: 22 June 1999
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| 48 | **
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| 49 | ** Copyright P.T.Wallace. All rights reserved.
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| 50 | */
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| 51 |
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| 52 | #define AS2R 0.484813681109535994e-5 /* arcseconds to radians */
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| 53 |
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| 54 | {
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| 55 | /* FK5 to Hipparcos orientation and spin (radians, radians/year) */
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| 56 | static double ortn[3] = { -19.9e-3 * AS2R,
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| 57 | -9.1e-3 * AS2R,
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| 58 | 22.9e-3 * AS2R },
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| 59 | s5[3] = { -0.30e-3 * AS2R,
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| 60 | 0.60e-3 * AS2R,
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| 61 | 0.70e-3 * AS2R };
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| 62 |
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| 63 | double p5e[3], r5h[3][3], t, vst[3], rst[3][3], p5[3], ph[3], w;
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| 64 | int i;
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| 65 |
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| 66 |
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| 67 | /* FK5 barycentric position vector. */
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| 68 | slaDcs2c ( r5, d5, p5e );
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| 69 |
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| 70 | /* FK5 to Hipparcos orientation matrix. */
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| 71 | slaDav2m ( ortn, r5h );
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| 72 |
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| 73 | /* Time interval from epoch to J2000. */
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| 74 | t = 2000.0 - epoch;
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| 75 |
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| 76 | /* Axial vector: accumulated Hipparcos wrt FK5 spin over that interval. */
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| 77 | for ( i = 0; i < 3; i++ ) {
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| 78 | vst [ i ] = s5 [ i ] * t;
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| 79 | }
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| 80 |
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| 81 | /* Express the accumulated spin as a rotation matrix. */
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| 82 | slaDav2m ( vst, rst );
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| 83 |
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| 84 | /* Derotate the vector's FK5 axes back to epoch. */
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| 85 | slaDimxv ( rst, p5e, p5 );
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| 86 |
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| 87 | /* Rotate the vector into the Hipparcos frame. */
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| 88 | slaDmxv ( r5h, p5, ph );
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| 89 |
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| 90 | /* Hipparcos vector to spherical. */
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| 91 | slaDcc2s ( ph, &w, dh );
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| 92 | *rh = slaDranrm ( w );
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| 93 | }
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