public static function Atic13($ri, $di, $date1, $date2, &$rc, &$dc, &$eo) {
    /* Star-independent astrometry parameters */
    $astrom = new iauASTROM();

    /* Star-independent astrometry parameters. */
    IAU::Apci13($date1, $date2, $astrom, $eo);

    /* CIRS to ICRS astrometric. */
    IAU::Aticq($ri, $di, $astrom, $rc, $dc);

    /* Finished. */
  }