NGC6553
 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)=    19.768 +-  0.134
 a(1)=     1.903 +-  0.212
 a(2)=     0.277 +-  0.167
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=1+(r/r_c), r_c=1.56
 a(0)=     8.2577
 a(1)=     0.9076
 a(2)=     0.7207
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set