3 Comparison with previous results

Several objects presented here were previously studied by Lilly & Prestage (1987, LP87) and Smith & Heckman (1989a,b, SH89). In common between our and LP87 samples there are 13 objects (0255+058, 0325+023, 0427-539, 0430+052, 0453-206, 0620-526, 0625-354, 0625-536, 0915-118, 0945+076, 1318-434, 1333-337, and 2221-023), while eight are in common with SH89 (0255+058, 0325+023, 0430+052, 0945+076, 1251-122, 1717-009, 1949+023, and 2221-023).

LP87 give Cousins metric R magnitudes for a fixed aperture of 19.2 kpc (for H₀=50 km s^-1 Mpc^-1), whereas SH89 report V and B bands isophotal (m₂₅) magnitudes. In order to perform an external check on our photometry, we derived metric R magnitudes at 19.2 kpc and isophotal magnitudes V₂₅ (assuming V-R=0.6 as appropriate for low redshift elliptical galaxies) for the common objects (Fig. 4), finding on average:

$<\Delta R_{19.2}>_{\rm LP87}\ = -0.12$ mag $~ ({\rm rms} = 0.29)$

$<\Delta V_{25}>_{\rm SH89}\ = 0.02$ mag $~ ({\rm rms} = 0.36)$ .

It is worth noticing that 0255+058 and 1251-122 are dumbbell galaxies, while a bright, edge-on spiral galaxy projects on-top of 1318-434. The measure of the luminosity of these galaxies is therefore particularly difficult and dependent on the details of the adopted measuring strategy. Not surprisingly 0255+058 is the object with the largest discrepancy with respect to SH89. If we remove this object, the scatter becomes 0.27 and 0.19 for the comparison with LP87 and SH89, respectively. As a whole, our photometry agrees on average with previous photometry within $\sim 0.1$ magnitudes.

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Figure 1: Isophotal contour plots of the central portion of the Cousins R band CCD image of selected sources. The optical counterpart of the radio source is always placed at the center of the figure. The image scale is indicated; North is up and East to the left. Contours start at the surface brightness indicated on top of each panel, and are separated by 0.5 mag/arcsec²

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Figure 2: Contour plots for all dumbbell systems, together with those of the two members as obtained after they have been separated using a two-galaxy fitting procedure (Paper I). Objects are, from top to bottom, 0255+058, 0427-539, 0452-190, 0625-536, and 1251-122

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Figure 3: Morphological and photometric profiles as a function of the semimajor axis a^1/4 (arcsec). From top to bottom we report: surface brightness $\mu$ (mag/arcsec²); ellipticity $\epsilon$ ; major axis position angle PA in degree from North to East; Fourier coefficients c4. When not visible, the 1 $\sigma$ error bars are smaller than plotted symbol

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Figure 4: a) Magnitude differences between Lilly & Prestage (1987) and this work, versus our magnitudes. To compare these data we derived the aperture magnitudes at 19.2 kpc from our photometry. In common with data published by LP87, the magnitudes are corrected for galactic extinction. b) Magnitude differences between Smith & Heckman (1989a,b) and this work, versus our magnitudes. To compare these values we corrected our data for the different band of observation (assuming V-R=0.6) and transformed our total magnitudes ( $m_{\rm tot}$ ) into isophotal magnitudes (m₂₅). No correction for galactic extinction has been applied

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