!# $J$ filter (<-> $B_J$?) from Kron (1980), ApJS 43, 305.
"JK" 
"energy"       
"Vega"    0.
 3600.   0.000
 3650.   0.105
 3700.   0.184
 3750.   0.325
 3800.   0.467
 3850.   0.564
 3900.   0.662
 3950.   0.704
 4000.   0.745
 4050.   0.753
 4100.   0.761
 4150.   0.741
 4200.   0.722
 4250.   0.703
 4300.   0.684
 4350.   0.689
 4400.   0.695
 4450.   0.716
 4500.   0.737
 4550.   0.754
 4600.   0.770
 4650.   0.778
 4700.   0.787
 4750.   0.792
 4800.   0.798
 4850.   0.808
 4900.   0.818
 4950.   0.842
 5000.   0.866
 5050.   0.913
 5100.   0.960
 5150.   0.980
 5200.   1.000
 5250.   0.888
 5300.   0.776
 5350.   0.561
 5400.   0.346
 5450.   0.238
 5500.   0.129
 5550.   0.082
 5600.   0.035
 5650.   0.018
 5700.   0.000
