NGC6558       c
 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)=    18.521 +-  0.146
 a(1)=     2.568 +-  0.263
 a(2)=     0.381 +-  0.210
 a(3)=    -0.152 +-  0.194
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=r
 a(0)=     7.4873
 a(1)=     1.2416
 a(2)=     1.2717
 a(3)=    -0.3505
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set