NGC6517
 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)=    20.604 +-  0.110
 a(1)=     3.204 +-  0.182
 a(2)=     0.342 +-  0.156
 a(3)=     0.181 +-  0.147
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=1+(r/r_c), r_c=0.80
 a(0)=     7.2538
 a(1)=     2.3161
 a(2)=    -0.6645
 a(3)=     0.2151
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set