NGC6981 (M72)
12 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)=    22.281 +-  0.146
 a(1)=     4.373 +-  0.236
 a(2)=     1.090 +-  0.176
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=1+(r/r_c), r_c=1.38
 a(0)=     7.8573
 a(1)=     0.0085
 a(2)=     1.0099
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set