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slalib/subet.f

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+      SUBROUTINE sla_SUBET (RC, DC, EQ, RM, DM)
+*+
+*     - - - - - -
+*      S U B E T
+*     - - - - - -
+*
+*  Remove the E-terms (elliptic component of annual aberration)
+*  from a pre IAU 1976 catalogue RA,Dec to give a mean place
+*  (double precision)
+*
+*  Given:
+*     RC,DC     dp     RA,Dec (radians) with E-terms included
+*     EQ        dp     Besselian epoch of mean equator and equinox
+*
+*  Returned:
+*     RM,DM     dp     RA,Dec (radians) without E-terms
+*
+*  Called:
+*     sla_ETRMS, sla_DCS2C, sla_,DVDV, sla_DCC2S, sla_DRANRM
+*
+*  Explanation:
+*     Most star positions from pre-1984 optical catalogues (or
+*     derived from astrometry using such stars) embody the
+*     E-terms.  This routine converts such a position to a
+*     formal mean place (allowing, for example, comparison with a
+*     pulsar timing position).
+*
+*  Reference:
+*     Explanatory Supplement to the Astronomical Ephemeris,
+*     section 2D, page 48.
+*
+*  P.T.Wallace   Starlink   10 May 1990
+*
+*  Copyright (C) 1995 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 RC,DC,EQ,RM,DM
+
+      DOUBLE PRECISION sla_DRANRM,sla_DVDV
+      DOUBLE PRECISION A(3),V(3),F
+
+      INTEGER I
+
+
+
+*  E-terms
+      CALL sla_ETRMS(EQ,A)
+
+*  Spherical to Cartesian
+      CALL sla_DCS2C(RC,DC,V)
+
+*  Include the E-terms
+      F=1D0+sla_DVDV(V,A)
+      DO I=1,3
+         V(I)=F*V(I)-A(I)
+      END DO
+
+*  Cartesian to spherical
+      CALL sla_DCC2S(V,RM,DM)
+
+*  Bring RA into conventional range
+      RM=sla_DRANRM(RM)
+
+      END