these wavelengths provide essential complementary information for studying stellar warps.

Sample
======

Our sample was selected by de Grijs (1997, 1998) from the Surface Photometry Catalogue of the ESO-Uppsala Galaxies (ESO-LV; Lauberts & Valentijn 1989). This catalogue contains large numbers of galaxies that have been selected and parameterised uniformly. The galaxies were originally selected on ESO-Schmidt survey plates covering declinations $\delta \le -17.5^\circ$, excluding the area within $15^\circ$ of the Galactic Equator, at Galactic latitudes $|b| < 15^\circ$. We selected 20 candidate galaxies from a statistically complete diameter-limited subsample of edge-on disc galaxies (de Grijs 1997, 1998), with the following characteristics (see Table 1):

-   $D_{25} (B) \geq 2.2'$, i.e., with optical diameters (at a surface brightness level of $\mu_{B} = 25$ mag arcsec$^{-2}$) larger than $2.2'$;

-   Isolated galaxies, i.e., without significant neighbours within a distance greater than or equal to five times their optical diameters. They should be classified as noninteracting and undisturbed;

-   Inclination, $i > 87^\circ$;

-   Morphological type range from S0 to Sd, i.e., revised Hubble types later than T $= -2$ (spiral and lenticular galaxies).

The inclinations were determined assuming an intrinsic flattening $(b/a)_{0} = 0.11$ (de Grijs 1997, 1998), so that our sample 