1 /*
2 *+
3 * Name:
4 * palFk54z
5
6 * Purpose:
7 * Convert a J2000.0 FK5 star position to B1950.0 FK4 assuming
8 * zero proper motion and parallax.
9
10 * Language:
11 * Starlink ANSI C
12
13 * Type of Module:
14 * Library routine
15
16 * Invocation:
17 * palFk54z( double r2000, double d2000, double bepoch, double *r1950,
18 * double *d1950, double *dr1950, double *dd1950 )
19
20 * Arguments:
21 * r2000 = double (Given)
22 * J2000.0 FK5 RA (radians).
23 * d2000 = double (Given)
24 * J2000.0 FK5 Dec (radians).
25 * bepoch = double (Given)
26 * Besselian epoch (e.g. 1950.0).
27 * r1950 = double * (Returned)
28 * B1950 FK4 RA (radians) at epoch "bepoch".
29 * d1950 = double * (Returned)
30 * B1950 FK4 Dec (radians) at epoch "bepoch".
31 * dr1950 = double * (Returned)
32 * B1950 FK4 proper motion (RA) (radians/trop.yr)).
33 * dr1950 = double * (Returned)
34 * B1950 FK4 proper motion (Dec) (radians/trop.yr)).
35
36 * Description:
37 * This function converts star positions from the IAU 1976,
38 * FK5, Fricke system to the Bessel-Newcomb, FK4 system.
39
40 * Notes:
41 * - The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt.
42 * - Conversion from Julian epoch 2000.0 to Besselian epoch 1950.0
43 * only is provided for. Conversions involving other epochs will
44 * require use of the appropriate precession functions before and
45 * after this function is called.
46 * - The FK5 proper motions, the parallax and the radial velocity
47 * are presumed zero.
48 * - It is the intention that FK5 should be a close approximation
49 * to an inertial frame, so that distant objects have zero proper
50 * motion; such objects have (in general) non-zero proper motion
51 * in FK4, and this function returns those fictitious proper
52 * motions.
53 * - The position returned by this function is in the B1950
54 * reference frame but at Besselian epoch BEPOCH. For comparison
55 * with catalogues the "bepoch" argument will frequently be 1950.0.
56
57 * Authors:
58 * PTW: Pat Wallace (STFC)
59 * DSB: David Berry (JAC, Hawaii)
60 * {enter_new_authors_here}
61
62 * History:
63 * 2012-02-13 (DSB):
64 * Initial version with documentation taken from Fortran SLA
65 * Adapted with permission from the Fortran SLALIB library.
66 * {enter_further_changes_here}
67
68 * Copyright:
69 * Copyright (C) 1995 Rutherford Appleton Laboratory
70 * Copyright (C) 2012 Science and Technology Facilities Council.
71 * All Rights Reserved.
72
73 * Licence:
74 * This program is free software: you can redistribute it and/or
75 * modify it under the terms of the GNU Lesser General Public
76 * License as published by the Free Software Foundation, either
77 * version 3 of the License, or (at your option) any later
78 * version.
79 *
80 * This program is distributed in the hope that it will be useful,
81 * but WITHOUT ANY WARRANTY; without even the implied warranty of
82 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
83 * GNU Lesser General Public License for more details.
84 *
85 * You should have received a copy of the GNU Lesser General
86 * License along with this program. If not, see
87 * <http://www.gnu.org/licenses/>.
88
89 * Bugs:
90 * {note_any_bugs_here}
91 *-
92 */
93
94 #include "pal.h"
95 #include "pal1sofa.h"
96
palFk54z(double r2000,double d2000,double bepoch,double * r1950,double * d1950,double * dr1950,double * dd1950)97 void palFk54z( double r2000, double d2000, double bepoch, double *r1950,
98 double *d1950, double *dr1950, double *dd1950 ){
99
100 /* Local Variables: */
101 double r, d, px, rv, y;
102
103 /* FK5 equinox J2000 (any epoch) to FK4 equinox B1950 epoch B1950. */
104 palFk524( r2000, d2000, 0.0, 0.0, 0.0, 0.0, &r, &d, dr1950, dd1950,
105 &px, &rv );
106
107 /* Fictitious proper motion to epoch "bepoch". */
108 y = bepoch - 1950.0;
109 *r1950 = r + *dr1950*y;
110 *d1950 = d + *dd1950*y;
111
112 }
113
114