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SUBROUTINE sla_FK5HZ (R5,D5,EPOCH,RH,DH)
*+
* - - - - - -
* F K 5 H Z
* - - - - - -
*
* Transform an FK5 (J2000) star position into the frame of the
* Hipparcos catalogue, assuming zero Hipparcos proper motion.
*
* (double precision)
*
* This routine converts a star position from the FK5 system to
* the Hipparcos system, in such a way that the Hipparcos proper
* motion is zero. Because such a star has, in general, a non-zero
* proper motion in the FK5 system, the routine requires the epoch
* at which the position in the FK5 system was determined.
*
* Given:
* R5 d FK5 RA (radians), equinox J2000, epoch EPOCH
* D5 d FK5 Dec (radians), equinox J2000, epoch EPOCH
* EPOCH d Julian epoch (TDB)
*
* Returned (all Hipparcos):
* RH d RA (radians)
* DH d Dec (radians)
*
* Called: sla_DCS2C, sla_DAV2M, sla_DIMXV, sla_DMXV, sla_DCC2S,
* sla_DRANRM
*
* Notes:
*
* 1) The FK5 to Hipparcos transformation consists of a pure
* rotation and spin; zonal errors in the FK5 catalogue are
* not taken into account.
*
* 2) The published orientation and spin components are interpreted
* as "axial vectors". An axial vector points at the pole of the
* rotation and its length is the amount of rotation in radians.
*
* 3) See also sla_FK52H, sla_H2FK5, sla_HFK5Z.
*
* Reference:
*
* M.Feissel & F.Mignard, Astron. Astrophys. 331, L33-L36 (1998).
*
* P.T.Wallace Starlink 22 June 1999
*
* Copyright (C) 1999 Rutherford Appleton Laboratory
*-
IMPLICIT NONE
DOUBLE PRECISION R5,D5,EPOCH,RH,DH
DOUBLE PRECISION AS2R
PARAMETER (AS2R=0.484813681109535994D-5)
* FK5 to Hipparcos orientation and spin (radians, radians/year)
DOUBLE PRECISION EPX,EPY,EPZ
DOUBLE PRECISION OMX,OMY,OMZ
PARAMETER ( EPX = -19.9D-3 * AS2R,
: EPY = -9.1D-3 * AS2R,
: EPZ = +22.9D-3 * AS2R )
PARAMETER ( OMX = -0.30D-3 * AS2R,
: OMY = +0.60D-3 * AS2R,
: OMZ = +0.70D-3 * AS2R )
DOUBLE PRECISION P5E(3),ORTN(3),R5H(3,3),T,VST(3),RST(3,3),
: P5(3),PH(3),W
DOUBLE PRECISION sla_DRANRM
* FK5 barycentric position vector.
CALL sla_DCS2C(R5,D5,P5E)
* FK5 to Hipparcos orientation matrix.
ORTN(1) = EPX
ORTN(2) = EPY
ORTN(3) = EPZ
CALL sla_DAV2M(ORTN,R5H)
* Time interval from epoch to J2000.
T = 2000D0-EPOCH
* Axial vector: accumulated Hipparcos wrt FK5 spin over that interval.
VST(1) = OMX*T
VST(2) = OMY*T
VST(3) = OMZ*T
* Express the accumulated spin as a rotation matrix.
CALL sla_DAV2M(VST,RST)
* Derotate the vector's FK5 axes back to epoch.
CALL sla_DIMXV(RST,P5E,P5)
* Rotate the vector into the Hipparcos frame.
CALL sla_DMXV(R5H,P5,PH)
* Hipparcos vector to spherical.
CALL sla_DCC2S(PH,W,DH)
RH = sla_DRANRM(W)
END
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