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eraPmpx

pco = ERFA.pmpx(rc, dc, pr, pd, px, rv, pmt, pob)

Proper motion and parallax.

Given:

   rc,dc  double     ICRS RA,Dec at catalog epoch (radians)
   pr     double     RA proper motion (radians/year, Note 1)
   pd     double     Dec proper motion (radians/year)
   px     double     parallax (arcsec)
   rv     double     radial velocity (km/s, +ve if receding)
   pmt    double     proper motion time interval (SSB, Julian years)
   pob    double[3]  SSB to observer vector (au)

Returned:

   pco    double[3]  coordinate direction (BCRS unit vector)

Notes:

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

  2. The proper motion time interval is for when the starlight reaches the solar system barycenter.

  3. To avoid the need for iteration, the Roemer effect (i.e. the small annual modulation of the proper motion coming from the changing light time) is applied approximately, using the direction of the star at the catalog epoch.

References:

1984 Astronomical Almanac, pp B39-B41.

Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to the Astronomical Almanac, 3rd ed., University Science Books (2013), Section 7.2.

Called:

   eraPdp       scalar product of two p-vectors
   eraPn        decompose p-vector into modulus and direction

This revision: 2021 April 3

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