NGC6397       c
 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)=    19.361 +-  0.079
 a(1)=     5.102 +-  0.150
 a(2)=     1.880 +-  0.112
 a(3)=     0.492 +-  0.114
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=r
 a(0)=     6.3907
 a(1)=     0.6987
 a(2)=    -0.1640
 a(3)=     0.3181
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set