NGC6626 (M28)
 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)=    18.432 +-  0.071
 a(1)=     2.699 +-  0.113
 a(2)=     0.259 +-  0.093
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=1+(r/r_c), r_c=1.28
 a(0)=     6.7750
 a(1)=     1.3296
 a(2)=     0.3315
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set