!# $M$ filter from Bessel & Brett (1988), PASP 100, 1134.
"M"
"energy"       
"Vega"    0.
44800.   0.000
45000.   0.470
45200.   0.680
45400.   0.640
45600.   0.600
45800.   0.690
46000.   0.780
46200.   0.890
46400.   1.000
46600.   0.940
46800.   0.880
47000.   0.600
47200.   0.320
47400.   0.510
47600.   0.700
47800.   0.680
48000.   0.660
48200.   0.700
48400.   0.740
48600.   0.810
48800.   0.880
49000.   0.810
49200.   0.740
49400.   0.600
49600.   0.460
49800.   0.300
50000.   0.140
50200.   0.100
50400.   0.060
50600.   0.030
50800.   0.000
