NGC6809 (M55)
 8 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)=    22.192 +-  0.116
 a(1)=     3.886 +-  0.190
 a(2)=     1.098 +-  0.168
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=1+(r/r_c), r_c=2.05
 a(0)=     8.3084
 a(1)=    -0.4346
 a(2)=     1.5897
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set