4 Discussion

4.1 Integrated magnitudes and colours

The estimated magnitudes and colours of the galaxies in the sample are presented in Table 3. Entries are as follows: Col. (1) gives the identification in Karachentsev Catalogue, Cols. (2) to (5) give the observed total integrated magnitudes in B, V, R and I bands, Cols. (6) and (7) give the observed (B-V) and (B-I) colour indices. Finally Cols. (8) and (9) give the total corrected $B_{\rm T}^{0}$ magnitude and $(B-V)_{\rm T}^{0}$colour index in the RC3 system. LogR₂₅ and the galactic absorption A_B were taken from RC3 Catalogue and Burstein & Heiles (1982), respectively. As stated above, total typical uncertainties in our photometry are 0.15, 0.14, 0.15 and 0.14 for B, V, R and I bands.

Magnitude and colour corrections were not applied for a few small galaxies (blank spaces in Table) in the neighborhood of our pairs, due to a lack of reliable information. Our observations span a range (11, 15.9) and (0.3, 1.1) mag in $B_{\rm T}^{0}$ and $(B-V)_{\rm T}^{0}$, respectively. The observed (B-V) range is comparable (by judging the colour maps scales) to that in a similarly selected sample of pairs in the southern hemisphere by Reduzzi & Rampazzo (1996), although some E/S0 components were included in that sample. Interestingly, our $(B-V)_{\rm T}^{0}$ range is comparable to the full range found in Larson & Tinsley (1978) in spite of the fact that their interacting sample is biased in favour of strongly peculiar systems from the Arp's catalogue. Similarly, the photoelectric Cousins UBVRI photometry of interacting galaxies by Johansson & Bergvall (1990) shows a comparable range in the observed (B-V) colours, although this sample is biased in favour of disturbed morphology, the presence of bridges and includes a fraction of E/S0 components.

4.2 The Holmberg effect

As a byproduct of his famous photometric survey of nearby galaxies, Holmberg (1958) compared the photographic colours of paired galaxies and found a significant correlation between the colours of pair components. This phenomenon has since been referred to as the "Holmberg effect''. Figure 4 shows the correlation between the $(B-V)_{\rm T}^{0}$ colour index. In a few cases irregular galaxies belonging to pairs have conventionally been considered as spirals. The colour index along the vertical axis refers to the brighter (primary) component and that along the horizontal axis refers to the fainter (secondary) component in each pair. To reinforce the validity of any correlation, other symbols indicate sources of $(B-V)_{\rm T}^{0}$ data for additional (S+S) Karachentsev pairs from the literature.

Figure 4: The Holmberg effect. $(B-V)^{0}_{\rm T}$ primary versus $(B-V)^{0}_{\rm T}$ secondary.

The colour correlation between pair components is tight. A correlation coefficient $r \sim 0.77$ with a residual sigma of 0.18 is obtained for our (S+S) data. Additionally, a fitting to all the data in Fig. 4, give a correlation coefficient $r \sim 0.70$ with a residual sigma of 0.18. All the (S+S) pairs with (B-V) either from our observations or from the literature, have a median relative velocity, $\Delta v \sim 45$ km s^-1 and a median projected separation $\Delta x \sim 29$ kpc. Although the physical explanation of the Holmberg effect is complex, it has been interpreted as reflecting a tendency for similar types of galaxies to form together (morphological concordance), a possible reflection of the role of local environment in determining galaxy morphology, but alternatively, it can presumably also reflect mutually induced star formation (Kennicutt et al. 1987) in physical pairs.

4.3 Colours and morphology

To discuss the optical morphology (that could be modified by the presence of bars, spiral arms, rings, etc.) and its relationship to the global photometrical properties, the final results for each pair are presented in the form of a mosaic (Fig. A.1) including: 1) mean azimuthally averaged surface brightness and colour profiles, 2) gray scale B-band images, 3) (B-I) colour index maps and 4) B band-filtered images for each pair. In most of the cases, not all the foreground stars in each field have been removed. The images in the lower panels 3) and 4) can be combined to look for morphological features like the presence of bars, rings, the shape of spiral arms, the presence of tidal features and other morphological distortions presumably associated with the interactions. The filtered/enhancing techniques (Sofue 1993 applied in 4), allow the subtraction of the diffuse background in a convenient way to discuss different morphological details.

Karachentsev (1972) identified three basic interaction classes (AT, LI and DI) that describe the pairs which show obvious signs of interaction. AT class identifies pairs with components in a common luminous halo with a symmetric, amorphous or shredded, asymmetric (sh) structure. LI pairs show evidence of tidal bridges (br), tails (ta) or both (br+ta). DI pairs show evidence of structural distortion in one (1) or both (2) components. We add to this sequence NI for the (S+S) pairs with no obvious morphological distortion. The order AT-LI-DI-NI can be regarded as a sequence from strongest to weakest evidence for tidal distortion or, alternatively, most to least dynamically evolved (interpreting a common envelope as a sign of extensive dynamical evolution in pairs).

Based on our CCD observations, it is now possible to attempt 1) a reclassification of the Hubble morphology from a combination of our colour index (B-I) maps and sharp/filtered B images, 2) a reclassification of the global pair interaction morphology (I/A class hereafter) in the Karachentsev Catalogue and 3) a reclassification of the spiral arm morphology as suggested by Elmegreen & Elmegreen (1982) (hereafter EE class).

It is known that the colours of spiral galaxies are correlated with its morphological type T. Although the colour indices of galaxies belonging to type T will have a large dispersion, the median value declines systematically as T increases along the morphological sequence. Median integrated total (B-V) colours of galaxies according to morphological class are given by Roberts & Haynes (1994). The UGC and the Local Supercluster (LSc) samples in Roberts & Haynes (1994) are rather inhomogeneous in terms of environment, but the interacting objects were excluded from their analysis. We may consider these samples as comparison/reference samples for the following discussion.

4.4 Comments on individual objects

Before proceeding to a discussion of the results shown in tables and figures, we present comments on morphological details found in individual pairs that may be relevant to our conclusions and look for any relationship to the global photometrical profiles.

KPG64A. The galaxy is classified as SA(s)b pec. Our (B-I) colour map shows two centrally symmetric spiral arms that become bifurcated at the outer parts. The arms are sharp-defined and the B-band sharp/filtered image can show some well-defined knotty structures along them. A bright small nucleus can also be appreciated. We classify this galaxy as Sc pec. The type of arms shown may probably be produced/modified by the interaction as predicted by simulations in Noguchi (1990). The total $(B-V)_{\rm T}^{0}$ colour is representative of Sab-Sb types. Our EE class is 6.

KPG64B. The galaxy is classified as SB(s)a pec. Our (B-I) colour map shows an apparently inclined galaxy that could be simulating a barred structure in the central region of a lower resolution image. The outer spiral structure resembles an integral sign that could be tidally generated by the interaction, on line with simulations by Noguchi (1990). The sharp/filtered image shows a faint bifurcated structure emanating from the eastern arm. There is also evidence of knotty structure along the arms, but no clear evidence of a bar structure. We classify this galaxy as Sbc. The total $(B-V)_{\rm T}^{0}$ colour is more representative of S0a-Sa types. We notice that the colour profiles tend to be flat after 15 $\hbox{$^{\prime\prime}$ }$. Our EE class is 6. The I/A class for the pair is LI. KPG68A. This galaxy is overlapping at the southeast with its companion. Our iterative modeling of the light distribution is poor and caution is needed with the total magnitudes and colours for both galaxies. The galaxy is classified as a Scd:. Our sharp/filtered and B-I colour map images shows a bright nucleus plus multiple arms with knotty structure along them. The total $(B-V)_{\rm T}^{0}$ colour is representative of Sb-Sbc types. Our EE class is 3.

KPG68B. This galaxy is overlapping at the north with its companion. The galaxy is classified as a SBb:. Our sharp/filtered and B-I colour map images shows knotty structure along the arms from either end of a prominent bar. The total $(B-V)_{\rm T}^{0}$ colour is representative of Sb-Sbc types. The colour profiles in this barred galaxy are flat after 5 $\hbox{$^{\prime\prime}$ }$ from its center. The I/A class for the pair is DI. Our EE class is 10.

KPG75A. The galaxy is classified as E?, but our (B-I)and sharp/filtered images show a bright central nucleus from which two opened and diffuse spiral arms emanate. The spiral pattern shows an integral sign (perhaps as a by product of the interaction). We classify this galaxy as Sab. The $(B-V)_{\rm T}^{0}$ colour is representative of S0a-Sa types.

KPG75B. The galaxy is classified as SB?, and our (B-I)and sharp/filtered images show a bright nucleus and two wrapped adjacent spiral arms that in projection may simulate a bar. We cannot clearly identify a bar structure. The arm at the north appears warped. We classify this galaxy as Sb. The $(B-V)_{\rm T}^{0}$ colour is representative of Sab-Sb types. The I/A class for the pair is DI. Our EE class is 7.

KPG88A. The galaxy is classified as a SA(s)c and our (B-I) and sharp/filtered images shows a few bright knots along multiple arms that emanate from a bright nucleus. The $(B-V)_{\rm T}^{0}$ colour is redder than that corresponding to its morphological type. Our estimated (B-V) colour is consistent, however, with that reported by Prugniel & Héraudeau (1998). The colour profiles tend to be flat after 15 $\hbox{$^{\prime\prime}$ }$. Our EE class is 12.

KPG88B. The galaxy is classified as a SBcd:. Both our sharp/filtered and (B-I) colour map show a prominent bar and complex arms extending from either end. The $(B-V)_{\rm T}^{0}$ colour is redder than that corresponding to its morphological type. The I/A class for the pair is DI. Our EE class is 10.

KPG98A. The galaxy is classified as Scd:. Our (B-I) and sharp/filtered images show a bright nucleus plus a perturbed spiral pattern that seems warped in projection. A few knots can be seen along the arms. The $(B-V)_{\rm T}^{0}$ colour is bluer than that corresponding to its morphological type. We caution the reader about an aparent inconsistency in the results obtained for this pair. Contrary to the observed (B-V) value, the corresponding colour profiles show a tendency to be redder. After repeating the calculations and taking into account our estimated errors in B and V magnitudes, we do not have an explantion for this behaviour. Our EE class is 2.

KPG98B. This galaxy is classified as S?. Our (B-I)and sharp/filtered images show a prominent nucleus plus a faint but defined spiral pattern that simulates an outer pseudo-ring structure. This pattern could be reminiscent of the interaction with its companion. We classify this galaxy as (R)Sa. The $(B-V)_{\rm T}^{0}$ colour is redder than that corresponding to its morphological type. RC3 Catalogue reports (only) a blue photographic magnitude with an error of 0.2 mag that was transformed to the standard system. However, this value is within 0.2 mag to ours. The I/A class for the pair is DI.

KPG102A. This galaxy is classified as Sa. Our (B-I) and sharp/filtered images show a prominent nuclear structure from which a diffuse wrapped spiral pattern emerges. We classify the galaxy as SBab. The $(B-V)_{\rm T}^{0}$ colour is bluer than that corresponding to its morphological type.

KPG102B. The galaxy is classified as Sb and our (B-I) and sharp/filtered images show a bright nuclear region plus a beautiful symmetric and sharply-defined spiral pattern that could be caused by the interaction with its companion. We classify the galaxy as Sc. The $(B-V)_{\rm T}^{0}$ colour is bluer than that corresponding to its morphological type. The (B-R) and (B-I) colour profiles have a tendency to be flat after 10 $\hbox{$^{\prime\prime}$ }$. The I/A class for the pair is LI. Our EE class is 11.

KPG103A. The galaxy is classified as Sb. Its small angular size make the visualization of features a difficult task. At our resolution, both the (B-I) and sharp/filtered images shows a peculiar morphology. Keel (1988) has extensively studied this galaxy. The $(B-V)_{\rm T}^{0}$ colour is representative of a Sab-Sb galaxy. The (B-V) colour profile have a tendency to be flat along the observed radius.

KPG103B. The galaxy is classified as Sa. At our resolution, the (B-I), sharp/filtered and unsharp masking images show a peculiar morphology. The arms appear radially distributed from a prominent bulge. Keel (1988) has extensively studied this galaxy. The $(B-V)_{\rm T}^{0}$ colour is representative of a Scd-Sd galaxy. The I/A class for the pair is DI.

KPG108A. The galaxy is classified as Sbc. Our (B-I) and sharp/filtered images show a highly inclined galaxy with a bright elongated bulge and a complex dusty structure. It is difficult to find definite signs of perturbation. The $(B-V)_{\rm T}^{0}$ colour is redder than that corresponding to its morphological type. RC3 Catalogue reports (only) a blue photographic magnitude with an error of 0.2 mag that was transformed to the standard system. However, this value is within 0.2 mag to ours. The (B-R) and (B-V) colour profiles have a tendency to be flat after 25 $\hbox{$^{\prime\prime}$ }$.

KPG108B. The galaxy is classified as Sb. Our (B-I) and sharp/filtered images show a highly inclined galaxy with a complex dusty structure. It is difficult to trace signs of perturbation. A small galaxy (north-east) in its neighborhood can be appreciated. The $(B-V)_{\rm T}^{0}$ colour is redder than that corresponding to its morphological type. RC3 Catalogue reports (only) a blue photographic magnitude with an error of 0.2 mag that was transformed to the standard system. However, this value is within 0.2 mag to ours. The colour profiles have a tendency to be flat after 30 $\hbox{$^{\prime\prime}$ }$. The I/A class for the pair is NI.

KPG112A. The galaxy is classified as S0/a. Our sharp/filtered and B-I images show and edge-on galaxy resembling a lenticular or an early-type spiral with a distorted disk. The distorted disk may be representing a tidal tail/counter-tail structure generated by the interaction. We classify this galaxy as Sa. The $(B-V)_{\rm T}^{0}$ colour is representative of Sab-Sb types. The (B-V) and (B-R) colour profiles tend to be flat after 10 $\hbox{$^{\prime\prime}$ }$, while the (B-I) colour profile appear flat all along the observed radius.

KPG112B. The galaxy is classified as S0:. Our sharp/filtered and B-I images show a bright prominent bulge. Two diffuse spiral arms appear wrapped. The arms at the west side are seen, in projection, overlapping at the eastern arm of its companion galaxy. We classify this galaxy as Sa. The $(B-V)_{\rm T}^{0}$ colour is representative of a Sa galaxy. Our EE class is 12. The I/A class for the pair is LI.

KPG125A. The galaxy is classified as Pec. In spite of its small angular size, our (B-I) and sharp/filtered images show two faint spiral arms emerging from a complex and bright central region. We classify this galaxy as Sab pec. The estimated $(B-V)_{\rm T}^{0}$ colour is representative of Sab-Sb types. The colour profiles in this galaxy show a tendency to be flat after 5 $\hbox{$^{\prime\prime}$ }$.

KPG125B. The galaxy is classified as S pec. However, both our (B-I) and sharp/filtered images show multiple and complex spiral arms with knotty features along them and emanating from a bright nuclear region. We classify this galaxy as Sc pec. The estimated $(B-V)_{\rm T}^{0}$ colour is representative of Sab-Sb types. The colour profiles show a tendency to be flat after 20 $\hbox{$^{\prime\prime}$ }$. The I/A class for the pair is DI. Our EE class is 9.

KPG136A. This galaxy is classified as S?. Our (B-I) and sharp/filtered images show a bright central region from which multiple but diffuse arms appear to emanate. We classify this galaxy as Sbc. The estimated $(B-V)_{\rm T}^{0}$ colour is representative of Sbc-Sc types. Our EE class is 10.

KPG136B. This galaxy is classified as S?. Our (B-I) and sharp/filtered images show a bright nuclear region surrounded by a tightly wrapped arm-like structure resembling a ring or pseudo-ring. An outer faint feature also resembles a diffuse shell/arc that may be associated with a tidal origin. We classify the galaxy as S(r)ab. The $(B-V)_{\rm T}^{0}$ colour is representative of a Sa type. The I/A class for the pair is DI. Our EE class is 8.

KPG141A. The galaxy is classified as S?. Our (B-I) and sharp/filtered images show a highly inclined galaxy where a central bulge and a few knots along a thin linear feature (arm seen in projection?) at the north-east can be appreciated. We classify this galaxy as Sbc. The $(B-V)_{\rm T}^{0}$ colour is redder than that representative of its morphological type. RC3 Catalogue reports (only) a blue photographic magnitude with an error of 0.3 mag that was transformed to the standard system. However, this value is within 1.1 mag of ours.

KPG141B. The galaxy is classified as S?. Our (B-I) and sharp/filtered images show a bright prominent central region and two wrapped but defined arms. We classify this galaxy as Sb. The estimated $(B-V)_{\rm T}^{0}$ colour is redder than that representative of its morphological type. RC3 Catalogue reports (only) a blue photographic magnitude with an error of 0.3 mag that was transformed to the standard system. However, this value is within 0.3 mag to ours. The I/A class for the pair is DI. Our EE class is 7.

KPG150A. The galaxy is classified as Sa. Our (B-I) and sharp/filtered images show an internal two-arm spiral pattern and a bright nucleus. An outer spiral arm pattern is wrapped and may be resembling, in projection, a pseudo-ring. We classify this galaxy as SA(r)b. The estimated $(B-V)_{\rm T}^{0}$colour is representative of S0-S0a types. Our EE class is 7.

KPG150B. The galaxy is classified as SBb. Our (B-I) and sharp/filtered images show a sharply defined bar and multiple knotty arms wrapped enough in the central region to resemble an internal ring. We classify this galaxy as SB(r)c. The colour profiles (in the presence of a bright nearby field star) do not show a tendency to be flat like other barred galaxies in this sample. The estimated $(B-V)_{\rm T}^{0}$ colour is redder than that representative of its morphological type. Prugniel & Héraudeau (1998) report a blue magnitude in agreement (for a similar aperture) to ours. RC3 Catalogue reports (only) a blue total magnitude with an error of 0.15 mag that was transformed to the standard system. However, this value is within 0.2 mag to ours. The I/A class for the pair is NI. Our EE class is 8.

KPG151A. The galaxy is seen slightly overlapping, in projection, to its companion galaxy at the south-east. The galaxy is classified as Sc. Our (B-I) and sharp/filtered images show an edge-on galaxy with a clearly defined bulge region. The estimated $(B-V)_{\rm T}^{0}$ colour is redder than that corresponding to its morphological type. We could not find a reference in the literature with which to compare magnitudes and colours for this source.

KPG151B. The galaxy is classified as SB?. Our (B-I) and sharp/filtered images show a bright prominent nuclear region and an adjacent elongated feature that resembles a bar. We classify this galaxy as SBb. The $(B-V)_{\rm T}^{0}$ colour is redder than that corresponding to its morphological type. RC3 Catalogue reports (only) a blue photographic magnitude with an error of 0.2 mag that was transformed to the standard system. However, this value is within 0.1 mag of ours. The (B-V) colour profile shows a marginal tendency to be flat after 20 $\hbox{$^{\prime\prime}$ }$. The I/A class for the pair is LI. Our EE class is 8.

KPG156A. The galaxy is classified as SA(r)c pec. Our sharp/filtered and (B-I) images show a bright central nucleus surrounded by two knotty arms forming an inner ring structure. The arms extend far from the center forming: 1) a bridge to its companion and 2) a very long tail. They may be tidally-generated by the interaction. In addition, faint filamentary structures are seen almost tangent to the ring. The estimated $(B-V)_{\rm T}^{0}$ colour is definitely bluer than that corresponding to its morphological type. Our EE class is 11.

KPG156B. The galaxy is classified as SB(rs)c pec. However, in our sharp/filtered and (B-I) images no clear ringed structure is noticed. We notice instead, a bright and somehow elongated nuclear region with two diffuse and opened spiral arms resembling a integral sign. We classify this galaxy as SBbc pec. The estimated $(B-V)_{\rm T}^{0}$ colour is representative of Sbc-Sc types. The (B-R) and (B-I) colour profiles show a tendency to be flat after 15 $\hbox{$^{\prime\prime}$ }$. The I/A class for the pair is LI.

KPG159A. The galaxy is classified as Sb. The small angular size of this galaxy does not allow both the sharp/filtered and (B-I) images to show any detailed morphology. The $(B-V)_{\rm T}^{0}$ colour is representative of Sm-Im types.

KPG159B. The galaxy is classified as Sb. The sharp/filtered and (B-I) images shows an inclined galaxy with a bright nuclear region and wrapped spiral arms. A faint linear feature crossing the central region resembles a bar. We classify this galaxy as SBb. The $(B-V)_{\rm T}^{0}$ colour is representative of Sb-Sbc types. The I/A class for the pair is DI.

KPG160A. The galaxy is classified as SB(s)a. Our (B-I) and sharp/filtered images show a bright outer ring enclosing a bar-like feature. The outer ring is bluer than the adjacent disk. We classify this galaxy as (R')SB(s)a. The $(B-V)_{\rm T}^{0}$ colour is representative of S0a-Sa types. The colour profiles show a tendency to be flat after 25 $\hbox{$^{\prime\prime}$ }$. Our EE class is 8.

KPG160B. The galaxy is classified as SBa. Our (B-I) and sharp/filtered images show a highly inclined system where it is difficult to see the bar and bulge regions. There is knotty structure along the main body of the galaxy. We classify this galaxy as Sb. The $(B-V)_{\rm T}^{0}$ colour is representative of Sa-Sab types. If the outer ring in the companion galaxy is regarded as evidence of interaction, the I/A class for the pair is DI, otherwise is NI.

KPG168A. The galaxy is classified as Sa. Our (B-I) and sharp/filtered images show a prominent bulge region and two symmetric spiral arms that simulate a pseudo-ring. In the external parts, the arms are extended and diffuse (resembling an integral sign) forming a bridge to the south-east of its companion galaxy. We classify this galaxy as S(s)b. The $(B-V)_{\rm T}^{0}$ colour is more representative of S0-S0a types. The colour profiles show a tendency to be flat from 40 $\hbox{$^{\prime\prime}$ }$. Our EE class is 6.

KPG168B. The galaxy is classified as Sc. Our (B-I) and sharp/filtered images show an apparently inclined system with a few prominent knots along the main body. Two adjacent diffuse arms are also appreciated. One of them is apparently forming a bridge at the west of its companion galaxy. The $(B-V)_{\rm T}^{0}$ colour is more representative of Sa-Sab types. The colour profiles show a tendency to be flat along most of the observed radius. The I/A class for the pair is LI.

KPG195A. The galaxy is classified as SB(s)a pec. The configuration of this pair resembles that of KPG168. Our (B-I) and sharp/filtered images show a prominent bulge and an adjacent linear feature that crosses the central region resembling a bar. From this bar, two spiral arms emerge. These arms are prominent in the central regions and become diffuse and extended (resembling an integral sign) at the external parts. We classify this galaxy as SB(s)b pec. The $(B-V)_{\rm T}^{0}$ colour is representative of S0a-Sa types The colour profiles show a marginal tendency to be flat after 40 $\hbox{$^{\prime\prime}$ }$. Our EE class is 6.

KPG195B. The galaxy is classified as SB(s)m? Our (B-I) and sharp/filtered images show an apparently inclined system with bright condensations along the main body and two adjacent arms that become diffuse at the outskirts. The bar structure is difficult to discerne. We classify this galaxy as Sc. The $(B-V)_{\rm T}^{0}$ colour is representative of Sbc-Sc types. The I/A class for the pair is DI.

KPG211A. The galaxy is classified as (R')SAB(rs)ab pec: and our (B-I) and sharp/filtered images seem to confirm this classification. The pattern of spiral arms is complex, tightly wrapped and shows blue colours. This could be a sign of strong perturbation from its companion. The estimated $(B-V)_{\rm T}^{0}$ is representative of S0-S0a types. The colour profiles show a tendency to be flat after 30 $\hbox{$^{\prime\prime}$ }$. Our EE class is 8.

KPG211B. The galaxy is classified as Sb: and our (B-I) and sharp/filtered images show an apparently inclined galaxy with a prominent bulge and two symmetric, diffuse spiral arms. We classify this galaxy as Sa. The $(B-V)_{\rm T}^{0}$ colour is representative of S0-S0a types. Our EE class is 7. The I/A class for the pair is DI.

KPG216A. The galaxy has a bright nearby field star that was difficult to subtract in our iterative procedure. The galaxy is classified as SB(s)b pec: Our (B-I) and sharp/filtered images show an elongated central region resembling a bar structure from which two diffuse spiral arms (integral sign) emerge. Our EE class is 10.

KPG216B. The galaxy is classified as SAB(s)c pec: Our (B-I) and sharp/filtered images show an elongated feature crossing the center and resembling a bar from which two knotty arms emanate. The arm at the west is multiple. We classify this galaxy as SBc pec. The $(B-V)_{\rm T}^{0}$ colour is representative of Sm-Im types. The colour profiles show structure and a global tendency to be flat after 35 $\hbox{$^{\prime\prime}$ }$. The I/A class for the pair is DI. Our EE class is 9.

KPG249A. The pair show an apparent low degree of overlapping. The galaxy is classified as SAB(rs)cd pec. Our sharp/filtered and (B-I) images show two bright condensations in the nuclear region. The arms show a bifurcated spiral pattern and knotty features. The arm at north-east is forming an apparent bridge to its companion galaxy. We classify this galaxy as SABcd pec. The $(B-V)_{\rm T}^{0}$ colour is more representative of Sm-Im types. The colour profiles show a tendency to be flat after 30 $\hbox{$^{\prime\prime}$ }$. Our EE class is 6.

KPG249B. The galaxy is classified as IBm pec. Our sharp/filtered and (B-I) images show some bright condensations along a main elongated body that resembles a bar structure from which two diffuse opened arms emerge. We classify this galaxy as SBm pec. The $(B-V)_{\rm T}^{0}$ colour is more representative of Sm-Im types. The colour profiles show a tendency to be flat along the observed radius. The I/A class for the pair is LI.

KPG295A. This is a low-degree overlapping pair where both components show remarkably similar morphological features. The galaxy is classified as SAB(rs)a pec and both our (B-I) and sharp/filtered images show a bright nuclear region and a faint adjacent broad feature that may be resembling a bar structure. These features are enclosed by an internal set of blue arms forming an elongated internal ring. In addition, this galaxy also shows an external diffuse and elongated ring. We classify this galaxy as (R')SAB(r)a pec. The $(B-V)_{\rm T}^{0}$ colour is representative of S0a-Sa types. Our EE class is 8.

KPG295B. The galaxy is classified as SAB(rs)ab pec. Our (B-I) and sharp/filtered images show a galaxy with a prominent nuclear region enclosed by two wrapped arms resembling an inner ring structure. The external arms are bright, blue and wrapped. The $(B-V)_{\rm T}^{0}$ colour is representative of Sab-Sb types. The I/A class for the pair is DI. Our EE class is 8.

KPG302A. The galaxy is classified as SAB(rs)c:. Our (B-I) and sharp/filtered images show a beautiful spiral structure with knotty blue features all along the arms. We cannot identify signs of a barred structure. We classify this galaxy as Sc. The $(B-V)_{\rm T}^{0}$ colour is representative of Sc-Scd types. Our EE class is 12.

KPG302B. The galaxy is classified as SB0/a pec. Our (B-I) and sharp/filtered show a prominent and elongated central region that may resemble a bar. Alternatively, we may interpret that as two overlapping bright central sources forming an elongated feature from which two diffuse spiral arms emanate. The arm towards the companion is apparently bifurcated forming an external arc/shell-like feature. We classify this galaxy as SBbc pec. The $(B-V)_{\rm T}^{0}$ colour is representative of Sd-Sm types. The colour profiles show a tendency to be flat all along its radius. The I/A class for the pair is DI. Our EE class is 6.

KPG313A. The galaxy is classified as SAB(rs)cd. Our (B-I) and sharp/filtered images show a central elongated bar-like feature that is enclosed by a set of arms with apparently differing pitch angles and resembling a broken ring. Blue knotty features are observed along the arms. The $(B-V)_{\rm T}^{0}$ colour is representative of Sb-Sbc types. The (B-I) colour profile show a tendency to be flat after 40 $\hbox{$^{\prime\prime}$ }$. Our EE class is 1.

KPG313B. The galaxy is classified as Sab:sp. Our sharp/filtered and (B-I) images show an inclined galaxy with extended and apparently warped arms. The $(B-V)_{\rm T}^{0}$ colour is redder than that corresponding to its morphological type. RC3 reports total asymptotic B and V magnitudes with associated errors of 0.15 mag that imply a (B-V) colour in agreement to our observed value. The I/A class for the pair is DI.

KPG332A. The galaxy is classified as SA(rs)c and our (B-I) and sharp/filtered images show a bright nucleus and blue knotty arms. We do not find evidence for an internal ring or s-shaped structure. We classify this galaxy as Sc. The $(B-V)_{\rm T}^{0}$ colour is representative of Sa type. Our EE class is 3.

KPG332B. The galaxy is classified as Sc: sp and our (B-I) and sharp/filtered images show a spectacular and complex dust lane structure all along the plane of the galaxy. The $(B-V)_{\rm T}^{0}$ colour is redder than that corresponding to its morphological type. RC3 reports total asymptotic B and V magnitudes with associated errors of 0.1 mag that imply a (B-V) colour in agreement with our observed value. The I/A class for the pair is NI.

KPG347A. The components in this pair show an apparent overlapping but similar morphological types. The galaxy is classified as SA(rs)bc. Our sharp/filtered and (B-I) images show a prominent bulge region and wrapped spiral arms that resemble an inner ring. Blue knotty features are seen along the arms. We classify this galaxy as SA(r)bc. The $(B-V)_{\rm T}^{0}$ colour is representative of Sa types. Our EE class is 12.

KPG347B. The galaxy is classified as SA(rs)bc. Our sharp/filtered and (B-I) images show an inclined galaxy with a bright nucleus and knotty features along multiple spiral arms. We classify this galaxy as Sc. The estimated $(B-V)_{\rm T}^{0}$ colour is representative of Sa types. The I/A class for the pair is DI. Our EE class is 3.

KPG389A. The components in this pair have similar morphological features (cf. KPG295) and their arms overlap in the outer region. The galaxy is classified as SAB(s)b pec and our (B-I) and sharp/filtered images show a very definite nucleus and an adjacent small spiral arm enclosed by two external arms. They are knotty and resemble an inner pseudo-ring but become diffuse at large radii. The east arm is seen interpenetrating the west arm of its companion such that an x-like feature is formed. We classify this galaxy as SA(rs)bpec. The $(B-V)_{\rm T}^{0}$ colour is representative of Sb-Sbc types. Our EE class is 6.

KPG389B. The galaxy is classified as SA(s)b: pec and our (B-I) and sharp/filtered images show an elongated nuclear region from which two long and diffuse arms emerge. The west arm appears crossing the east arm of its companion forming an x-shaped feature. We classify this galaxy as SABb pec. The $(B-V)_{\rm T}^{0}$ colour is representative of Sa-Sab types. The colour profiles show a tendency to be flat after 20 $\hbox{$^{\prime\prime}$ }$. The I/A class for the pair is LI. Our EE class is 7.

KPG396A. The galaxy is classified as SB(s)d: sp. Our (B-I) and sharp/filtered images show an apparently inclined system with an elongated nucleus and a spiral pattern that is difficult to trace. The $(B-V)_{\rm T}^{0}$ colour is more representative of Sm-Im types.

KPG396B. The galaxy is classified as SB(s)d. Our (B-I)and sharp/filtered images show a prominent bar structure and a complex, knotty spiral pattern with differing pitch angles. The $(B-V)_{\rm T}^{0}$ colour is representative of a Sm-Im types. The colour profiles show structure and a tendency to be flat after 25 $\hbox{$^{\prime\prime}$ }$. The I/A class for the pair is DI. Our EE class is 1.

KPG404A. The pair show an apparent low degree of overlapping. The galaxy is classified as SB(s)b pec. Our sharp/filtered and (B-I) images show a prominent nucleus and a faint adjacent linear bar from which two spiral arms (integral sign tidal arms) emanate. The arms are wrapped and simulate an inner ring structure. A third small galaxy can be seen near the end of the western arm (tail). The southern arm is seen forming a bridge to its companion galaxy. We classify this galaxy as SB(r)b pec. The $(B-V)_{\rm T}^{0}$ colour is representative of Sab-Sb types. The colour profiles show a tendency to be flat after 25 $\hbox{$^{\prime\prime}$ }$. Our EE class is 10.

KPG404B. The galaxy is classified as SA(s)b pec. Our sharp/filtered and (B-I) images show a bright nucleus and apparently strong dust lanes along the arms (see the arm towards the companion galaxy). The $(B-V)_{\rm T}^{0}$ colour is representative of Sab-Sb types. The I/A class for the pair is LI. Our EE class is 11.

KPG426A. The galaxy is classified as S?. Our (B-I) and sharp/filtered images show a prominent bulge and barred structure. At either end of the bar, strong condensations and two thin/faint and wrapped arms emanate. There is also indication of a ring enclosing the bar. We classify this galaxy as SB(r)b. The $(B-V)_{\rm T}^{0}$ colour is representative of S0-S0a types. The colour profiles show a tendency to be flat after 25 $\hbox{$^{\prime\prime}$ }$. Our EE class is 10.

KPG426B. The galaxy is classified as S?. Our (B-I) and sharp/filtered images show a prominent but elongated bulge region and a very faint spiral pattern. An unsharp masking image suggest that an arc-like structure may be present at the western external part. We classify this galaxy as SABb. The $(B-V)_{\rm T}^{0}$ colour is representative of S0a-Sa types. The I/A class for the pair is DI. Our EE class is 8.

KPG440A. The galaxy is classified as SAB(rs)d and our (B-I) and sharp/filtered images show a bright central bar and a multiple spiral pattern with knotty structure all along the arms. We classify this galaxy as SBcd. The $(B-V)_{\rm T}^{0}$ colour is definitely bluer than that corresponding to its morphological type. Our EE class is 6.

KPG440B. The galaxy is classified as SBc? and our (B-I) and sharp/filtered images show a very complex dust lane structure along the plane of the galaxy, similar to KPG332b. In our images it is difficult to trace the nuclear region, bulge or bar. The $(B-V)_{\rm T}^{0}$ colour is representative of E-S0 types. The I/A class for the pair is NI.

KPG455A. The galaxy is classified as SB(s)b and our (B-I) and sharp/filtered images show a bright nuclear region and two faint wrapped spiral arms resembling an inner ring. It is difficult to trace the presence of a bar, although the bulge region is elongated. The spiral pattern becomes diffuse at the outer parts. We classify this galaxy as SA(r)b. The $(B-V)_{\rm T}^{0}$ colour is representative of S0a-Sa types.

KPG455B. The galaxy is classified as SB(s)bc but our (B-I) and sharp/filtered images show a bright nucleus from which a spiral pattern emerge. A Blue knotty structure is observed along the arms. At our resolution, we have no clear evidence of a barred structure. We classify this galaxy as SA(s)bc. The $(B-V)_{\rm T}^{0}$ colour is representative of Sc-Scd types. The I/A class for the pair is DI. Our EE class is 7.

4.5 Results

Table 4 is a summary of the results found in this work. Column (1) gives the pair catalogued number, Col. (2) gives the Hubble Type as reported in NED, Col. (3) gives the Hubble Type as estimated in this work, Col. (4) gives the Elmegreen (EE) class, Col. (5) gives the revised Karachentsev interaction I/A class, Col. (6) shows when a flat colour profile is present, and finally Col. (7) remarks the presence of Bars, Knots, Rings and Shell structures.

 

 

Table 4: Final results from this study.

Galaxy pair	HUBBLE TYPE(NED)	HUBBLE TYPE(THIS WORK)	EE CLASS	I/A CLASS	PROFILE	NOTES
KPG64A	SA(s)b pec	Sc pec	6	LI		K
KPG64B	SB(s)a pec	Sbc	6		F	K
KPG68A	Scd:		3	DI		K
KPG68B	SBb:		10		F	B, K
KPG75A	E?	Sab		DI
KPG75B	SB?	Sb	7
KPG88A	SA(s)c		12	DI	F	K
KPG88B	SBcd:		10			B
KPG98A	Scd:		2	DI	F	K
KPG98B	S?	(R)Sa				R
KPG102A	Sa	SBab		LI		B
KPG102B	Sb	Sc	11		F
KPG103A	Sc			DI	F
KPG103B	Sa
KPG108A	Sbc			NI	F
KPG108B	Sb				F
KPG112A	S0/a	Sa		LI	F
KPG112B	S0:	Sa	12
KPG125A	Pec	Sab pec		DI	F
KPG125B	S pec	Sc pec	9		F	K
KPG136A	S?	Sbc	10	DI
KPG136B	S?	S(r)ab	8			R
KPG141A	S?	Sbc		DI		K
KPG141B	S?	Sb	7
KPG150A	Sa	S(r)b	7	NI		R
KPG150B	SBb	SB(r)c	8			B, K, R
KPG151A	Sc			LI
KPG151B	SB?	SBb	8		F	B
KPG156A	SA(r)c pec		11	LI		K, R
KPG156B	SB(rs)c pec	SBbc pec			F	B
KPG159A	Sb			DI
KPG159B	Sb	SBb				B
KPG160A	SB(s)a	(R')SB(s)a	8	DI	F	B, R
KPG160B	SBa	Sb				K
KPG168A	Sa	S(s)b	6	LI	F	R
KPG168B	Sc				F	K
KPG195A	SB(s)a pec	SB(s)b pec	6	DI	F	B
KPG195B	SB(s)m?	Sc				K
KPG211A	(R')SAB(rs)ab pec:		8	DI	F	B
KPG211B	Sb:	Sa	7
KPG216A	SB(s)b pec:		10	DI		B
KPG216B	SAB(s)c pec:	SBc pec	9		F	B
KPG249A	SAB(rs)cd pec	SABcd pec	6	LI	F	B, K
KPG249B	IBm pec	SBm pec			F	B, K
KPG295A	SAB(rs)a pec	(R')SAB(r)a pec	8	DI		B, R
KPG295B	SAB(rs)ab pec		8			B, R
KPG302A	SAB(rs)c:	Sc	12	DI		K
KPG302B	SB0/a pec	SBbc pec	6		F	B
KPG313A	SAB(rs)cd		1	DI	F	B, R, K
KPG313B	Sab:sp
KPG332A	SA(rs)c	Sc	3	NI		K
KPG332B	Sc: sp
KPG347A	SA(rs)bc		12	DI		K
KPG347B	SA(rs)bc	Sc	3			K
KPG389A	SAB(s)b pec	SA(rs)b pec	6	LI		K
KPG389B	SA(s)b: pec	SABb pec	7		F	B
KPG396A	SB(s)d: sp			DI		B
KPG396B	SB(s)d		1		F	B, K
KPG404A	SB(s)b pec	SB(r)b pec	10	LI	F	B, R

 

 

Table 4: continued.

Galaxy pair	HUBBLE TYPE(NED)	HUBBLE TYPE(THIS WORK)	EE CLASS	I/A CLASS	PROFILE	NOTES
KPG404B	SA(s)b pec		11
KPG426A	S?	SB(r)b	10	DI	F	B, R
KPG426B	S?	SABb	8			B, Sh
KPG440A	SAB(rs)d	SBcd	6	NI		B, K
KPG440B	SBc?					B
KPG455A	SB(s)b	SA(r)b		DI		R
KPG455B	SB(s)bc	SA(s)bc	7			K

F = Flat Colour Profile.
B = Bar.
K = Presence of Knots.
R = Ring.
Sh = Shell.

A reclassification of the galaxies in the (S+S) sample was made using our CCD data. The original classifications were made on the low resolution POSS. We revise the Hubble classifications for at least one component in 44% of our pairs (29 galaxies). An appreciable change in Hubble types $\Delta T \geq 2$ was found in 25 galaxies. The bulk of the sample is comprised of (S+S) pairs. Very few galaxies could be classified as irregular, and they may well be severely distorted spirals. If we consider $\Delta T \geq 2$ as a minimum value for morphological discordance in pairs, then half of our pairs show morphological concordance between pair members; 17 pairs (51%) show $\Delta T \sim 1$ and 16 pairs (49%) $\Delta T \geq 2$. This could explain, in part, the strong correlation found between (B-V) colour indices (Holmberg Effect) between members of this sample.

Elmegreen & Elmegreen (1982) developed a 12-division morphological system to classify spiral galaxies according to the regularity of their spiral arm structure. This spiral arm classification correlates with the presence of density waves as in grand design galaxies. Following that work, we succeeded in classifying 43 spirals. Some of the spirals in the global sample are nearly edge-on, strongly interacting or simply do not fit into the Elmegreen & Elmegreen classes. From 26 barred spirals, 18 are grand design and only 2 are flocculent. From 40 non-barred galaxies, 17 are grand design and 5 are flocculent. Grand design structure seems to be connected with binary galaxies, but strongly for barred than for non-barred galaxies. These results seem to be consistent with those of Elmegreen & Elmegreen (1982). We also have found knotty features in 24 galaxies and have detected rings or pseudo-ring features in 13 galaxies.

Interestingly, a fraction of the spirals have "open arms'' that could be interpreted in the framework of the simulations of Noguchi (1990 and references therein). The simulated galaxies have sizes similar to those in our sample. Noguchi's models follow both the stellar and gaseous component evolution in a disc galaxy during the encounter. Briefly speaking, in this scenario of moderate interactions, the bar develops quite soon and it is long-lasting, while the ring develops later and the gas follows the configuration of the ring. Four different phases may be seen: 1) open arms appear (integral sign) after perigalacticon, 2) a bar develops, the arms start to close and the gas start to follow the star configuration, 3) the arms are completely closed around the bar and form a ring; the gas is mainly concentrated in the center and ring, and 4) the ring starts to be disrupted by the dynamics and the overall appearance of the galaxy becomes nearly asymmetric.

As noted above, a fraction of the spirals in our sample (40%/20%) show (bar/ring) features which could be a transient phenomenon of the interaction in Noguchi's models. The bars are always redder while the rings and knots are always bluer compared with the galaxy outskirts. Most of the bridges and tails maintain the colour of the outskirts of the galaxies. The knotty structure along the arms and disks confirms the global nature of the star formation induced by the interactions. From 33 pairs, 20 can be classified according to the I/A class DI, 9 pairs as LI, and 4 pairs as NI. We have not detected any AT class, perhaps as a selection bias from our observing strategy. The sequence AT-LI-DI-NI has been interpreted as a sequence going from strongest to weak for tidal distortion or from most to least dynamically evolved. According to this, our (S+S) pairs are mainly involved in interactions of moderate level.

An interesting correlation has been found between the optical morphology and the global photometric properties in these pairs. From 26 barred galaxies, 15 show a flat behaviour (negligible gradient) in the azimuthally averaged colour profile while from 40 non-barred galaxies, 12 show flat colour profiles. This result may indicate that the bar acts unifying the stellar populations of the bulge and disk, in agreement with a secular evolutionary scenario, and consistent with the results in Gadotti & dos Anjos (2001) and Zaritsky et al. (1994) where barred spiral galaxies have flatter abundance gradients than unbarred spirals.