; Given type (string, e.g, "O"), subtype (float, e.g. 3)
; and class (integer), return R-I from
; AQ 4th ed
;

function aq_ri, type, subtype, class
  functionname = 'aq_ri'
  CASE class OF
    5: begin ; Main sequence
	    CASE type OF
		'O': begin 
			x = [5,9] & y = [-0.32, -0.32]
		     end
		'B': begin 
			x = [0,2,5,8] & y = [-0.29, -0.22, -0.16, -0.10]
		     end
		'A': begin 
			x = [0,2,5] & y = [-0.02, 0.01, 0.06]
		     end
		'F': begin 
			x = [0,2,5,8] & y = [0.17, 0.20, 0.24, 0.29]
		     end
		'G': begin 
			x = [0,2,5,8] & y = [0.31, 0.33, 0.35, 0.38]
		     end
		'K': begin 
			x = [0,2,5] & y = [0.42, 0.48, 0.63]
		     end
		'M': begin 
			x = [0,2,5] & y = [0.91, 1.19, 1.67]
		     end
	  ENDCASE
       end
    3: begin ; giants. Teff for O-F are from xx
	    CASE type OF
		'G': begin 
			x = [5,8] & y = [0.48, 0.48]
		     end
		'K': begin 
			x = [0,2,5] & y = [0.53, 0.58, 0.90]
		     end
		'M': begin 
			x = [0,2,5] & y = [0.94, 1.10, 1.96]
		     end
		 ELSE: begin ; out of bounds! 
		    print, functionname+': spectral type out of bounds'
		    return, -100
		    end
	  ENDCASE
       end
    1: begin ; super giants. 
	    CASE type OF
		'B': begin 
 			   x = [2,5,8] 
			   y = [-0.15, -0.07, 0.00]
		     end
		'A': begin 
			x = [0,2,5] & y = [0.05, 0.07, 0.13]
		     end
		'F': begin 
			x = [0,2,5,8] & y = [0.20, 0.21, 0.23, 0.27]
		     end
		'G': begin 
			x = [0,2,5,8] & y = [0.33, 0.40, 0.44, 0.46]
		     end
		'K': begin 
			x = [0,2,5] & y = [0.48, 0.55, 0.90]
		     end
		'M': begin 
			x = [0,2,5] & y = [0.94, 1.10, 1.96]
		     end
		  ELSE: begin ; out of bounds! 
		    print, functionname+': spectral type out of bounds'
		    return, -100
		    end
	  ENDCASE
       end
  ELSE: begin ; out of bounds! 
    print, functionname+': spectral type out of bounds'
    return, -100
    end
  ENDCASE

  res = poly_fit(x, y, 1) 
  color = poly(subtype,res)
  return, color
end