NGC6218 (M12)
 6 iterations.
Chebyshev coeffients a(0)T_0(u)+a(1)T_1(u)+..., where u is log (r/arcsec) mapped to [-1,1]
 a(0)=    21.713 +-  0.115
 a(1)=     4.607 +-  0.188
 a(2)=     1.114 +-  0.165
 a(3)=     0.224 +-  0.148
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=1+(r/r_c)^2, r_c=1.68
 a(0)=     7.1383
 a(1)=     1.4557
 a(2)=    -0.2095
 a(3)=     0.2708
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set