.help refco Jun99 "Slalib Package"
.nf

      SUBROUTINE slRFCO (HM, TDK, PMB, RH, WL, PHI, TLR, EPS,
     :                      REFA, REFB)

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      R F C O
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  Determine the constants A and B in the atmospheric refraction
  model dZ = A tan Z + B tan**3 Z.

  Z is the "observed" zenith distance (i.e. affected by refraction)
  and dZ is what to add to Z to give the "topocentric" (i.e. in vacuo)
  zenith distance.

  Given:
    HM      d     height of the observer above sea level (metre)
    TDK     d     ambient temperature at the observer (deg K)
    PMB     d     pressure at the observer (millibar)
    RH      d     relative humidity at the observer (range 0-1)
    WL      d     effective wavelength of the source (micrometre)
    PHI     d     latitude of the observer (radian, astronomical)
    TLR     d     temperature lapse rate in the troposphere (degK/metre)
    EPS     d     precision required to terminate iteration (radian)

  Returned:
    REFA    d     tan Z coefficient (radian)
    REFB    d     tan**3 Z coefficient (radian)

  Called:  slRFRO

  Notes:

  1  Typical values for the TLR and EPS arguments might be 0.0065D0 and
     1D-10 respectively.

  2  The radio refraction is chosen by specifying WL > 100 micrometres.

  3  The routine is a slower but more accurate alternative to the
     slRFCQ routine.  The constants it produces give perfect
     agreement with slRFRO at zenith distances arctan(1) (45 deg)
     and arctan(4) (about 76 deg).  It achieves 0.5 arcsec accuracy
     for ZD < 80 deg, 0.01 arcsec accuracy for ZD < 60 deg, and
     0.001 arcsec accuracy for ZD < 45 deg.

  P.T.Wallace   Starlink   3 June 1997

  Copyright (C) 1997 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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