3 Results and errors

The thicknesses (H), inclinations ($\gamma$) and winding parameters ($\Lambda$) of 71 northern spiral galaxies are listed in Tables 1 and 2. Some other parameters are also listed: m is the number of arms, T the mean numerical Hubble stage index, $\mu$ $(=\arctan(m/\Lambda$)) the pitch angle of a spiral arm, h the apparent thickness, d the distance, H/D₀ the flatness, D₀ is the isophotal major diameter corrected to the "face-on'' ($\gamma=0^{\circ}$), and for Galactic extinction, but not for redshift.

  

Table 1: Thicknesses and inclinations of 71 northern spiral galaxies

  

Table 2: Thicknesses and inclinations of 71 northern spiral galaxies

The errors arise mainly from: a) the position of the innermost point for the arm; b) the inclination of the galaxy; c) the position of the galactic center. The errors from b) and c), however, can be reduced if we properly modify the grey-scale of the image by using IRAF to obtain the fine structure of the galaxy as deeply as possible. The estimations of error are derived from the formulae given by Peng (1988).