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80 lines
2.2 KiB
Fortran
80 lines
2.2 KiB
Fortran
SUBROUTINE sla_ETRMS (EP, EV)
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*+
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* - - - - - -
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* E T R M S
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* - - - - - -
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*
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* Compute the E-terms (elliptic component of annual aberration)
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* vector (double precision)
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*
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* Given:
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* EP dp Besselian epoch
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*
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* Returned:
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* EV dp(3) E-terms as (dx,dy,dz)
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*
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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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*
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* References:
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* 1 Smith, C.A. et al., 1989. Astr.J. 97, 265.
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* 2 Yallop, B.D. et al., 1989. Astr.J. 97, 274.
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*
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* P.T.Wallace Starlink 23 August 1996
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*
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* Copyright (C) 1996 Rutherford Appleton Laboratory
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*
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* License:
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program (see SLA_CONDITIONS); if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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* Boston, MA 02111-1307 USA
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*
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*-
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IMPLICIT NONE
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DOUBLE PRECISION EP,EV(3)
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* Arcseconds to radians
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DOUBLE PRECISION AS2R
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PARAMETER (AS2R=0.484813681109535994D-5)
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DOUBLE PRECISION T,E,E0,P,EK,CP
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* Julian centuries since B1950
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T=(EP-1950D0)*1.00002135903D-2
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* Eccentricity
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E=0.01673011D0-(0.00004193D0+0.000000126D0*T)*T
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* Mean obliquity
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E0=(84404.836D0-(46.8495D0+(0.00319D0+0.00181D0*T)*T)*T)*AS2R
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* Mean longitude of perihelion
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P=(1015489.951D0+(6190.67D0+(1.65D0+0.012D0*T)*T)*T)*AS2R
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* E-terms
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EK=E*20.49552D0*AS2R
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CP=COS(P)
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EV(1)= EK*SIN(P)
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EV(2)=-EK*CP*COS(E0)
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EV(3)=-EK*CP*SIN(E0)
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END
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