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

function aq_vk, type, subtype, class
  functionname = 'aq_vk'
  CASE class OF
    5: begin ; Main sequence
	    CASE type OF
		'O': begin 
			x = [9,9.5] & y = [-0.87,-0.85]
		     end
		'B': begin 
			x = [0,1,2,3,4,5,6,7,8,9] 
			y = [-0.83,-0.74,-0.66,-0.56,-0.49,-0.42,-0.36,-0.29,-0.24,-0.13]
		     end
		'A': begin 
			x = [0,2,5,7] & y = [0.00,0.14,0.38,0.50]
		     end
		'F': begin 
			x = [0,2,5,7] & y = [0.70,0.82,1.10,1.32]
		     end
		'G': begin 
			x = [0,2,4,6] & y = [1.41,1.46,1.53,1.64]
		     end
		'K': begin 
			x = [0,2,4,5,7]
			y = [1.96,2.22,2.63,2.85,3.16]
		     end
		'M': begin 
			x = [0,1,2,3,4,5,6] 
			y = [3.65,3.87,4.11,4.65,5.28,6.17,7.37]
		     end
	  ENDCASE
       end
    3: begin ; giants. Teff for O-F are from xx
	    CASE type OF
		'G': begin 
			x = [0,4,6,8] & y = [1.75,2.05,2.15,2.16]
		     end
		'K': begin 
			x = [0,1,2,3,4,5] & y = [2.31,2.50,2.70,3.00,3.26,3.60]
		     end
		'M': begin 
			x = [0,1,2,3,4,5,6,7]
			y = [3.85,4.05,4.30,4.64,5.10,5.96,6.84,7.80]
		     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 = [5,6,7,8,9] 
			   y = [-0.13,-0.07,0.01,0.07,0.13]
		     end
		'A': begin 
			x = [0,1,2,5] & y = [0.19,0.26,0.32,0.48]
		     end
		'F': begin 
			x = [0,2,5,8] & y = [0.64,0.75,0.93,1.21]
		     end
		'G': begin 
			x = [0,3,8] & y = [1.44,1.67,1.99]
		     end
		'K': begin 
			x = [0,1,2,3,5] & y = [2.15,2.28,2.43,2.90,3.50]
		     end
		'M': begin 
			x = [0,1,2,3,4] & y = [3.80,3.90,4.10,4.60,5.20]
		     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