6 Results from NIR data  

As for the optical images, the NIR frames also show that the inner region have the characteristic X-structure and that the disk is arc-bended toward West. Details of the data reduction are given in the Appendix E. We have extracted the light profiles along the same directions of the optical images and built the B-J, B-H, and B-K color profiles. This was realized by degrading the B-band image to the same seeing of the NIR images. They are shown in Figs. 12. The (J-H), (J-K), and (H-K) colors ( non plotted here) are constant, within the present uncertainty, up to the last measured point ($J-H = 0.70\pm0.05$, $J-K = 1.00\pm0.05$, $H-K = 0.30\pm0.05$).

A few comments are in order:
1) along the major axis the folded profiles do not match: the difference reaching up to $\sim$0.5 mag in (B-J), (B-H), and (B-K) at $r\sim$40'' from the center;
2) in the inner 3'' the (B-J), (B-H), and (B-K) color profiles along the major and intermediate axes have a small decrease ($\sim$0.15 mag), which is less evident along the minor axis. This reveals the presence of an elongated red component. In the same region the (B-R) color increases;
3) apart from the (B-R) color, the other colors are approximately constant with the distance from the center.

From the color indices we derived information about the dust distribution. By comparing the North and South semiaxes, we found that the color indexes $B-\lambda$ ($\lambda = V, R, J, H, K$) are systematically higher in the North direction, between 30'' and 60'', than in the South. We interpret the asymmetry as due to an enhancement of the average dust content in the region where the arm of the companion galaxy NGC 127 intercepts the major axis of NGC 128.

We computed the color excess $E(B-\lambda)$ by subtracting the corresponding color index of the two semiaxes, and, following the procedure described in Appendix F, we derived a dust mass excess of $\sim$$6\ 10^6~M_{\hbox{$\odot$}}$ associated to the North semiaxis. The IRAS data confirm that the dust is manly concentrated toward the region of interaction of the two galaxies (see Sect. 7) and, therefore, we may consider the derived dust mass as a measure of the dust content of NGC 128. Of course, adopting different models lower dust masses (up to one order of magnitude) can be obtained.

Taking into account the uncertainty in the color excess, the evaluation of the dust mass from the optical and NIR data is characterized by an error of $\sim$40%, a factor of two larger than those characterizing the FIR measurements.