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125 lines
3.7 KiB
Fortran
125 lines
3.7 KiB
Fortran
SUBROUTINE sla_FK5HZ (R5,D5,EPOCH,RH,DH)
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*+
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* - - - - - -
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* F K 5 H Z
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* - - - - - -
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*
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* Transform an FK5 (J2000) star position into the frame of the
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* Hipparcos catalogue, assuming zero Hipparcos proper motion.
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*
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* (double precision)
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*
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* This routine converts a star position from the FK5 system to
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* the Hipparcos system, in such a way that the Hipparcos proper
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* motion is zero. Because such a star has, in general, a non-zero
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* proper motion in the FK5 system, the routine requires the epoch
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* at which the position in the FK5 system was determined.
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*
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* Given:
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* R5 d FK5 RA (radians), equinox J2000, epoch EPOCH
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* D5 d FK5 Dec (radians), equinox J2000, epoch EPOCH
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* EPOCH d Julian epoch (TDB)
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*
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* Returned (all Hipparcos):
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* RH d RA (radians)
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* DH d Dec (radians)
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*
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* Called: sla_DCS2C, sla_DAV2M, sla_DIMXV, sla_DMXV, sla_DCC2S,
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* sla_DRANRM
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*
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* Notes:
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*
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* 1) The FK5 to Hipparcos transformation consists of a pure
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* rotation and spin; zonal errors in the FK5 catalogue are
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* not taken into account.
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*
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* 2) The published orientation and spin components are interpreted
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* as "axial vectors". An axial vector points at the pole of the
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* rotation and its length is the amount of rotation in radians.
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*
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* 3) See also sla_FK52H, sla_H2FK5, sla_HFK5Z.
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*
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* Reference:
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*
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* M.Feissel & F.Mignard, Astron. Astrophys. 331, L33-L36 (1998).
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*
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* P.T.Wallace Starlink 22 June 1999
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*
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* Copyright (C) 1999 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 R5,D5,EPOCH,RH,DH
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DOUBLE PRECISION AS2R
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PARAMETER (AS2R=0.484813681109535994D-5)
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* FK5 to Hipparcos orientation and spin (radians, radians/year)
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DOUBLE PRECISION EPX,EPY,EPZ
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DOUBLE PRECISION OMX,OMY,OMZ
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PARAMETER ( EPX = -19.9D-3 * AS2R,
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: EPY = -9.1D-3 * AS2R,
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: EPZ = +22.9D-3 * AS2R )
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PARAMETER ( OMX = -0.30D-3 * AS2R,
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: OMY = +0.60D-3 * AS2R,
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: OMZ = +0.70D-3 * AS2R )
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DOUBLE PRECISION P5E(3),ORTN(3),R5H(3,3),T,VST(3),RST(3,3),
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: P5(3),PH(3),W
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DOUBLE PRECISION sla_DRANRM
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* FK5 barycentric position vector.
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CALL sla_DCS2C(R5,D5,P5E)
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* FK5 to Hipparcos orientation matrix.
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ORTN(1) = EPX
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ORTN(2) = EPY
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ORTN(3) = EPZ
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CALL sla_DAV2M(ORTN,R5H)
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* Time interval from epoch to J2000.
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T = 2000D0-EPOCH
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* Axial vector: accumulated Hipparcos wrt FK5 spin over that interval.
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VST(1) = OMX*T
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VST(2) = OMY*T
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VST(3) = OMZ*T
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* Express the accumulated spin as a rotation matrix.
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CALL sla_DAV2M(VST,RST)
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* Derotate the vector's FK5 axes back to epoch.
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CALL sla_DIMXV(RST,P5E,P5)
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* Rotate the vector into the Hipparcos frame.
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CALL sla_DMXV(R5H,P5,PH)
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* Hipparcos vector to spherical.
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CALL sla_DCC2S(PH,W,DH)
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RH = sla_DRANRM(W)
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END
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