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    Re: formula for refraction
    From: Dave Walden
    Date: 2007 May 01, 20:33 -0700

    The following short FORTRAN program reproduces the critical table for
    refraction from the NA.  It is NOT based on fitted equations.  It uses
    the canonical multilayer-ray-following method of Biot-Auber-Standish
    (Astronomical Journal,119,2472-2474,2000 May).  It calls the slREFRO
    program of Wallace based on the work of Hohenkerk (HMNAO. Sept 1984).
    http://stsdas.stsci.edu/cgi-bin/gethelp.cgi?refro.hlp
    You can change pressue, temp, humidity, etc to generate your own
    table.
    
        program dwrefracna
        implicit none
        real*8 ZOBS,HM,TDK,PMB,RH,WL,PHI,TLR,EPS,REF
        real*8 pi,xi,rlim
        print*,'from dwrefracna.f'
        pi=4.d0*datan(1.d0)
        print*,pi
        hm=0.d0
        phi=45.d0*pi/180.d0
    c na 2007 values
        tdk=273.15d0+10.d0
        pmb=1010.d0
        rh=0.80d0
        wl=0.50169d0
    c assume tlr .0065
        tlr=0.0065d0
        eps=1d-10
        rlim=+5.35d0
        do 4 xi=9.d0,90.d0,1.d0/60.d0
        zobs=pi/180.d0*(90.d0-xi)
        call slRFRO(ZOBS,HM,TDK,PMB,RH,WL,PHI,TLR,EPS,REF)
        ref=ref*180.d0/pi*60.d0
        if(ref.lt.rlim)then
            print'(i3,f4.0,f8.5)',int(xi-1.d0/60.d0)
         &       ,60.d0*(xi-1.d0/60.d0-int(xi-1.d0/60.d0))
            print'(8x,a1,f3.1)','-',rlim
            rlim=rlim-.1d0
        endif
    4   continue
        end
    
    
     from dwrefracna.f
      3.14159265
      9 55.
            -5.3
     10  7.
            -5.2
     10 20.
            -5.2
     10 32.
            -5.1
     10 46.
            -5.0
     10 59.
            -4.9
     11 14.
            -4.8
     11 29.
            -4.7
     11 44.
            -4.6
     12  0.
            -4.5
     12 17.
            -4.4
     12 35.
            -4.3
     12 53.
            -4.2
     13 12.
            -4.1
     13 32.
            -4.0
     13 53.
            -3.9
     14 16.
            -3.8
     14 39.
            -3.7
     15  3.
            -3.6
     15 29.
            -3.5
    
    etc.
    
    
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