NGC6638
 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)=    20.698 +-  0.446
 a(1)=     4.087 +-  0.813
 a(2)=     0.500 +-  0.633
 a(3)=    -0.173 +-  0.460
 a(4)=     0.026 +-  0.300
Power-of-x coeffients a(0)+a(1)x+a(2)x^2+..., where x=1+(r/r_c), r_c=1.21
 a(0)=     6.9612
 a(1)=     0.0749
 a(2)=     1.9585
 a(3)=    -0.5004
 a(4)=     0.0472
log r(arcsec)   mu_V    mu_V(fitted)  residual   weight  data set