NGC6139
 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)=    20.592 +-  0.148
 a(1)=     3.911 +-  0.260
 a(2)=     0.504 +-  0.179
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=1+(r/r_c)^2, r_c=0.99
 a(0)=     6.8866
 a(1)=     1.1040
 a(2)=     0.3425
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set