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

function aq_ub, type, subtype, class
  functionname = 'aq_ub'
  CASE class OF
    5: begin ; Main sequence
	    CASE type OF
		'O': begin 
			x = [5,9] & y = [-1.19, -1.12]
		     end
		'B': begin 
			x = [0,2,5,8] & y = [-1.08,-0.84, -0.58, -0.34]
		     end
		'A': begin 
			x = [0,2,5] & y = [-0.02,0.05,0.10]
		     end
		'F': begin 
			x = [0,2,5, 8] & y = [0.03, 0.00, -0.02, 0.02]
		     end
		'G': begin 
			x = [0,2,5,8] & y = [0.06, 0.12, 0.20, 0.30]
		     end
		'K': begin 
			x = [0,2,5] & y = [0.45, 0.64, 1.08]
		     end
		'M': begin 
			x = [0,2,5] & y = [1.22, 1.18, 1.24]
		     end
	  ENDCASE
       end
    3: begin ; giants. Teff for O-F are from xx
	    CASE type OF
		'G': begin 
			x = [5,8] & y = [0.56, 0.70]
		     end
		'K': begin 
			x = [0,2,5] & y = [0.84, 1.16, 1.81]
		     end
		'M': begin 
			x = [0,2,5] & y = [1.87, 1.89, 1.58]
		     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 = [-0.93, -0.72, -0.55]
		     end
		'A': begin 
			x = [0,2,5] & y = [-0.38, -0.25, -0.08]
		     end
		'F': begin 
			x = [0,2,5,8] & y = [0.15, 0.18, 0.27, 0.41]
		     end
		'G': begin 
			x = [0,2,5,8] & y = [0.52, 0.63, 0.83, 1.07]
		     end
		'K': begin 
			x = [0,2,5] & y = [1.17, 1.32, 1.80]
		     end
		'M': begin 
			x = [0,2,5] & y = [1.90, 1.95, 1.60]
		     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