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* Compute the E-terms vector
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* void palEtrms ( double ep, double ev[3] );
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* ev = double [3] (Returned)
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* E-terms as (dx,dy,dz)
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* Computes the E-terms (elliptic component of annual aberration)
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* Note the use of the J2000 aberration constant (20.49552 arcsec).
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* This is a reflection of the fact that the E-terms embodied in
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* existing star catalogues were computed from a variety of
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* aberration constants. Rather than adopting one of the old
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* constants the latest value is used here.
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* - Smith, C.A. et al., 1989. Astr.J. 97, 265.
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* - Yallop, B.D. et al., 1989. Astr.J. 97, 274.
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* PTW: Pat Wallace (STFC)
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* TIMJ: Tim Jenness (JAC, Hawaii)
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* {enter_new_authors_here}
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* Initial version with documentation taken from Fortran SLA
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* {enter_further_changes_here}
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* Copyright (C) 2012 Science and Technology Facilities Council.
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* All Rights Reserved.
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 3 of
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* the License, or (at your option) any later version.
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* This program is distributed in the hope that it will be
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* useful, but WITHOUT ANY WARRANTY; without even the implied
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* warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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* PURPOSE. See the GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
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* {note_any_bugs_here}
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void palEtrms ( double ep, double ev[3] ) {
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/* Use the J2000 aberration constant */
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const double ABCONST = 20.49552;
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double t, e, e0, p, ek, cp;
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/* Julian centuries since B1950 */
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t = (ep - 1950.) * .0100002135903;
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e = .01673011 - (t * 1.26e-7 + 4.193e-5) * t;
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e0 = (84404.836 - ((t * .00181 + .00319) * t + 46.8495) * t) *
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/* Mean longitude of perihelion */
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p = (((t * .012 + 1.65) * t + 6190.67) * t + 1015489.951) *
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ek = e * ABCONST * PAL__DAS2R;
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ev[1] = -ek * cp * cos(e0);
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ev[2] = -ek * cp * sin(e0);