public static function Atoc13($type, $ob1, $ob2, $utc1, $utc2, $dut1, $elong,
          $phi, $hm, $xp, $yp, $phpa, $tc, $rh, $wl, &$rc, &$dc) {

    $j;
    $astrom = new iauASTROM();
    $eo;
    $ri;
    $di;

    /* Star-independent astrometry parameters. */
    $j = IAU::Apco13($utc1, $utc2, $dut1, $elong, $phi, $hm, $xp, $yp, $phpa,
                    $tc, $rh, $wl, $astrom, $eo);

    /* Abort if bad UTC. */
    if ($j < 0)
      return j;

    /* Transform observed to CIRS. */
    IAU::Atoiq($type, $ob1, $ob2, $astrom, $ri, $di);

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

    /* Return OK/warning status. */
    return $j;

    /* Finished. */
  }