| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | void slaPm ( double r0, double d0, double pr, double pd,
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| 4 | double px, double rv, double ep0, double ep1,
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| 5 | double *r1, double *d1 )
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| 6 | /*
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| 7 | ** - - - - - -
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| 8 | ** s l a P m
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| 9 | ** - - - - - -
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| 10 | **
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| 11 | ** Apply corrections for proper motion to a star RA,Dec.
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| 12 | **
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| 13 | ** (double precision)
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| 14 | **
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| 15 | ** References:
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| 16 | ** 1984 Astronomical Almanac, pp B39-B41.
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| 17 | ** (also Lederle & Schwan, Astron. Astrophys. 134, 1-6, 1984)
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| 18 | **
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| 19 | ** Given:
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| 20 | ** r0,d0 double RA,Dec at epoch ep0 (rad)
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| 21 | ** pr,pd double proper motions: RA,Dec changes per year of epoch
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| 22 | ** px double parallax (arcsec)
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| 23 | ** rv double radial velocity (km/sec, +ve if receding)
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| 24 | ** ep0 double start epoch in years (e.g Julian epoch)
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| 25 | ** ep1 double end epoch in years (same system as ep0)
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| 26 | **
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| 27 | ** Returned:
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| 28 | ** *r1,*d1 double RA,Dec at epoch ep1 (rad)
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| 29 | **
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| 30 | ** Notes:
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| 31 | **
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| 32 | ** 1 The proper motions in RA are dRA/dt rather than cos(Dec)*dRA/dt,
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| 33 | ** and are in the same coordinate system as R0,D0.
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| 34 | **
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| 35 | ** 2 If the available proper motions are pre-FK5 they will be per
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| 36 | ** tropical year rather than per Julian year, and so the epochs
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| 37 | ** must both be Besselian rather than Julian. In such cases, a
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| 38 | ** scaling factor of 365.2422D0/365.25D0 should be applied to the
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| 39 | ** radial velocity before use.
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| 40 | **
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| 41 | ** Called: slaDcs2c, slaDcc2s, slaDranrm
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| 42 | **
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| 43 | ** Defined in slamac.h: DAS2R
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| 44 | **
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| 45 | ** Last revision: 19 January 2000
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| 46 | **
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| 47 | ** Copyright P.T.Wallace. All rights reserved.
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| 48 | */
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| 49 | {
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| 50 | /* Km/s to AU/year multiplied by arc seconds to radians */
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| 51 | static double vfr = ( 365.25 * 86400.0 / 149597870.0 ) * DAS2R;
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| 52 |
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| 53 | int i;
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| 54 | double w, em[3], t, p[3];
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| 55 |
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| 56 | /* Spherical to Cartesian */
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| 57 | slaDcs2c ( r0, d0, p );
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| 58 |
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| 59 | /* Space motion (radians per year) */
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| 60 | w = vfr * rv * px;
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| 61 | em[0] = - pr * p[1] - pd * cos ( r0 ) * sin ( d0 ) + w * p[0];
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| 62 | em[1] = pr * p[0] - pd * sin ( r0 ) * sin ( d0 ) + w * p[1];
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| 63 | em[2] = pd * cos ( d0 ) + w * p[2];
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| 64 |
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| 65 | /* Apply the motion */
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| 66 | t = ep1 - ep0;
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| 67 | for ( i = 0; i < 3; i++ )
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| 68 | p[i] = p[i] + (t * em[i]);
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| 69 |
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| 70 | /* Cartesian to spherical */
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| 71 | slaDcc2s ( p, r1, d1 );
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| 72 | *r1 = slaDranrm ( *r1 );
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| 73 | }
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