NGC6401
 3 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)=    21.073 +-  0.143
 a(1)=     2.622 +-  0.244
 a(2)=     0.252 +-  0.173
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=1+(r/r_c), r_c=1.28
 a(0)=     8.1652
 a(1)=     1.2816
 a(2)=     0.3182
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set