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diff --git a/ast/pal/palEtrms.c b/ast/pal/palEtrms.c
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+/*
+*+
+*  Name:
+*     palEtrms
+
+*  Purpose:
+*     Compute the E-terms vector
+
+*  Language:
+*     Starlink ANSI C
+
+*  Type of Module:
+*     Library routine
+
+*  Invocation:
+*     void palEtrms ( double ep, double ev[3] );
+
+*  Arguments:
+*     ep = double (Given)
+*        Besselian epoch
+*     ev = double [3] (Returned)
+*        E-terms as (dx,dy,dz)
+
+*  Description:
+*     Computes the E-terms (elliptic component of annual aberration)
+*     vector.
+*
+*     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.
+*
+*  See also:
+*     - Smith, C.A. et al., 1989.  Astr.J. 97, 265.
+*     - Yallop, B.D. et al., 1989.  Astr.J. 97, 274.
+
+*  Authors:
+*     PTW: Pat Wallace (STFC)
+*     TIMJ: Tim Jenness (JAC, Hawaii)
+*     {enter_new_authors_here}
+
+*  History:
+*     2012-02-12 (TIMJ):
+*        Initial version with documentation taken from Fortran SLA
+*        Adapted with permission from the Fortran SLALIB library.
+*     {enter_further_changes_here}
+
+*  Copyright:
+*     Copyright (C) 1996 Rutherford Appleton Laboratory
+*     Copyright (C) 2012 Science and Technology Facilities Council.
+*     All Rights Reserved.
+
+*  Licence:
+*     This program is free software: you can redistribute it and/or
+*     modify it under the terms of the GNU Lesser General Public
+*     License as published by the Free Software Foundation, either
+*     version 3 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 Lesser General Public License for more details.
+*
+*     You should have received a copy of the GNU Lesser General
+*     License along with this program.  If not, see
+*     <http://www.gnu.org/licenses/>.
+
+*  Bugs:
+*     {note_any_bugs_here}
+*-
+*/
+
+#include "pal.h"
+#include "palmac.h"
+
+void palEtrms ( double ep, double ev[3] ) {
+
+  /* Use the J2000 aberration constant */
+  const double ABCONST = 20.49552;
+
+  double t, e, e0, p, ek, cp;
+
+  /*  Julian centuries since B1950 */
+  t = (ep - 1950.) * .0100002135903;
+
+  /*  Eccentricity */
+  e = .01673011 - (t * 1.26e-7 + 4.193e-5) * t;
+
+  /*  Mean obliquity */
+  e0 = (84404.836 - ((t * .00181 + .00319) * t + 46.8495) * t) *
+    PAL__DAS2R;
+
+  /*  Mean longitude of perihelion */
+  p = (((t * .012 + 1.65) * t + 6190.67) * t + 1015489.951) *
+    PAL__DAS2R;
+
+  /*  E-terms */
+  ek = e * ABCONST * PAL__DAS2R;
+  cp = cos(p);
+  ev[0] = ek * sin(p);
+  ev[1] = -ek * cp * cos(e0);
+  ev[2] = -ek * cp * sin(e0);
+
+}