1 Introduction

We are investigating the star formation history of nearby early-type galaxies with fine structures. Galaxies are located in low density environments, i.e. shell galaxies are nearly isolated (Malin & Carter 1983) while pairs considered are typical inhabitants of the edges of super-clusters (see Karachentsev 1990). We wish to study the correlation between the star formation and the interaction events. The presence of fine structures in the main body morphology of the galaxies is widely believed to be a signature of such processes (see for a review Barnes & Hernquist 1992). In this paper we present the kinematics of the stellar and of the gaseous components of a sample of shell galaxies and pair members, whose spectro-photometric data have been presented in Longhetti et al. (1997a, Paper I).

The present kinematic data have been used for the correction of the line-strength indices in Paper I. Furthermore, they permit the identification of "bona fide'' signs of interaction. Encounters and kinematic signs among the pair member galaxies have been widely studied by Borne (1990 and reference therein) and Combes et al. (1995) using N-body simulations. Among the "bona fide'' signs of interaction they consider the U-shape of the stellar velocity profile. They interpret the U-shape in terms of the ongoing ablation of the outer parts between members during the encounter. Models developed by these authors can make definite predictions about the physical reality of interacting pairs, i.e. if they form bound or unbound systems. Balcell & Quinn (1990) simulations found that the accretion of a small satellite may cause a well recognizable dip in the stellar velocity dispersion profile.

The indication coming from the kinematics of the ionized gaseous component concerning the degree of the interaction is still debated. E.g. the counter-rotation of the gaseous component with respect to the stellar one is interpreted by the models either as the debris of a small accretion event (see Barnes & Hernquist 1992) or as a sign of a "weak interaction'' involving an inner disc (Hau & Thompson 1994). Following Phillips et al. (1986), the physical condition of the ionized gas component found in early-type galaxies could be interpreted into a LINER framework, i.e. from starbursts to AGN like objects (Ho 1996). Although the wavelength range covered by our data is limited to perform an accurate analysis of the relevant lines ratios through diagnostic diagrams, we attempt to investigate excitation level of the ionized gas of some objects. Since we are interested in the star formation history, gas physical conditions will also be discussed in this context.

The paper is organized as follows. Observations and data reduction are presented in Sect. 2. In Sect. 3 we discuss the comparison with the literature and individual results. In Sect. 4 the physical status of the gas and the presence of LINER activity is presented. Section 5 discusses the origin of the galaxies in terms of the merging hypothesis. Finally, we summarize our conclusions in Sect. 6.