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SUBROUTINE slETRM (EP, EV)
*+
* - - - - - -
* E T R M
* - - - - - -
*
* 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., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301 USA
*
* Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
*-
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
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