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eraHfk5z

[r5, d5, dr5, dd5] = ERFA.hfk5z(rh, dh, date1, date2)

Transform a Hipparcos star position into FK5 J2000.0, assuming zero Hipparcos proper motion.

Given:

   rh            double    Hipparcos RA (radians)
   dh            double    Hipparcos Dec (radians)
   date1,date2   double    TDB date (Note 1)

Returned (all FK5, equinox J2000.0, date date1+date2):

   r5            double    RA (radians)
   d5            double    Dec (radians)
   dr5           double    FK5 RA proper motion (rad/year, Note 4)
   dd5           double    Dec proper motion (rad/year, Note 4)

Notes:

  1. The TT date date1+date2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TT)=2450123.7 could be expressed in any of these ways, among others:
          date1          date2

       2450123.7           0.0       (JD method)
       2451545.0       -1421.3       (J2000 method)
       2400000.5       50123.2       (MJD method)
       2450123.5           0.2       (date & time method)

The JD method is the most natural and convenient to use in cases where the loss of several decimal digits of resolution is acceptable. The J2000 method is best matched to the way the argument is handled internally and will deliver the optimum resolution. The MJD method and the date & time methods are both good compromises between resolution and convenience.

  1. The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt.

  2. The FK5 to Hipparcos transformation is modeled as a pure rotation and spin; zonal errors in the FK5 catalogue are not taken into account.

  3. It was the intention that Hipparcos should be a close approximation to an inertial frame, so that distant objects have zero proper motion; such objects have (in general) non-zero proper motion in FK5, and this function returns those fictitious proper motions.

  4. The position returned by this function is in the FK5 J2000.0 reference system but at date date1+date2.

  5. See also eraFk52h, eraH2fk5, Fk5zhz.

Called:

   eraS2c       spherical coordinates to unit vector
   eraFk5hip    FK5 to Hipparcos rotation and spin
   eraRxp       product of r-matrix and p-vector
   eraSxp       multiply p-vector by scalar
   eraRxr       product of two r-matrices
   eraTrxp      product of transpose of r-matrix and p-vector
   eraPxp       vector product of two p-vectors
   eraPv2s      pv-vector to spherical
   eraAnp       normalize angle into range 0 to 2pi

Reference:

F.Mignard & M.Froeschle, 2000, Astron.Astrophys. 354, 732-739.

This revision: 2021 May 11

Copyright (C) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.