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slalib/etrms.f

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+      SUBROUTINE sla_ETRMS (EP, EV)
+*+
+*     - - - - - -
+*      E T R M S
+*     - - - - - -
+*
+*  Compute the E-terms (elliptic component of annual aberration)
+*  vector (double precision)
+*
+*  Given:
+*     EP      dp      Besselian epoch
+*
+*  Returned:
+*     EV      dp(3)   E-terms as (dx,dy,dz)
+*
+*  Note the use of the J2000 aberration constant (20.49552 arcsec).
+*  This is a reflection of the fact that the E-terms embodied in
+*  existing star catalogues were computed from a variety of
+*  aberration constants.  Rather than adopting one of the old
+*  constants the latest value is used here.
+*
+*  References:
+*     1  Smith, C.A. et al., 1989.  Astr.J. 97, 265.
+*     2  Yallop, B.D. et al., 1989.  Astr.J. 97, 274.
+*
+*  P.T.Wallace   Starlink   23 August 1996
+*
+*  Copyright (C) 1996 Rutherford Appleton Laboratory
+*
+*  License:
+*    This program is free software; you can redistribute it and/or modify
+*    it under the terms of the GNU General Public License as published by
+*    the Free Software Foundation; either version 2 of the License, or
+*    (at your option) any later version.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU General Public License for more details.
+*
+*    You should have received a copy of the GNU General Public License
+*    along with this program (see SLA_CONDITIONS); if not, write to the 
+*    Free Software Foundation, Inc., 59 Temple Place, Suite 330, 
+*    Boston, MA  02111-1307  USA
+*
+*-
+
+      IMPLICIT NONE
+
+      DOUBLE PRECISION EP,EV(3)
+
+*  Arcseconds to radians
+      DOUBLE PRECISION AS2R
+      PARAMETER (AS2R=0.484813681109535994D-5)
+
+      DOUBLE PRECISION T,E,E0,P,EK,CP
+
+
+
+*  Julian centuries since B1950
+      T=(EP-1950D0)*1.00002135903D-2
+
+*  Eccentricity
+      E=0.01673011D0-(0.00004193D0+0.000000126D0*T)*T
+
+*  Mean obliquity
+      E0=(84404.836D0-(46.8495D0+(0.00319D0+0.00181D0*T)*T)*T)*AS2R
+
+*  Mean longitude of perihelion
+      P=(1015489.951D0+(6190.67D0+(1.65D0+0.012D0*T)*T)*T)*AS2R
+
+*  E-terms
+      EK=E*20.49552D0*AS2R
+      CP=COS(P)
+      EV(1)= EK*SIN(P)
+      EV(2)=-EK*CP*COS(E0)
+      EV(3)=-EK*CP*SIN(E0)
+
+      END