function rat2therm, rat, low, low_chan

t0 = [12.491845, 218.01112, -934.86813, 3163.2752, -3855.9986]
t1 = [16.620411, 740.30382, -11465.639, 138675.38, -836516.29, 1958724.5]
t2 = [32.898724, 3469.8640, -202499.27, 8579822.0,-1.8615412e+08,1.5871689e+09]

e0 = [-10.864651, 2.0262085, -0.067086306, 0.0010843543, -6.8168758e-06]
e1 = [-14.461323, 1.8193244, -0.047813274, 0.00061546785, -3.0921852e-06]
e2 = [-13.159111, 1.1713024, -0.020954427, 0.00018764319, -6.8316848e-07,$
  1.6616541e-10]

if (low_chan eq 0) then begin
  if (rat lt .32 and rat gt .02) then begin
    ii = indgen(5)
    temp = total(rat^ii * t0(ii))
    em = total(e0(ii) * temp^ii)
    em = 1. / exp(em) * low
  endif else begin
    temp = 0.
    em = 0.
  endelse
endif
  
if (low_chan eq 1) then begin
  if (rat lt .14 and rat gt .005) then begin
    ii = indgen(6)
    temp = total(rat^ii * t1(ii))
    ii = indgen(5)
    em = total(e1(ii) * temp^ii) 
    em = 1. / exp(em) * low
  endif else begin
    temp = 0.
    em = 0.
  endelse
endif
  
if (low_chan eq 2) then begin
  if (rat gt .003 and rat lt .038) then begin
    ii = indgen(6)
    temp = total(rat^ii * t2(ii))
    em = total(e2(ii) * temp^ii) 
    em = 1. / exp(em) * low
  endif else begin
    temp = 0.
    em = 0.
  endelse
endif

therm = [temp, em]
return, therm 
end