1 Introduction

The structural similarity between disky ellipticals and S0 galaxies (Carter 1987; Capaccioli 1987; Bender 1988; Nieto 1988; Capaccioli et al. 1990) has been the subject of several photometric and kinematic studies in recent years. The fact that the largest isophotal deviations from perfect ellipses appear in the most elongated ellipticals (Bender et al. 1989a; Capaccioli et al. 1990; Nieto et al. 1991) supports the explanation that pointed isophotes in disky ellipticals are due to the presence of close to edge-on embedded disks. Rix & White (1990) studied in simulations the detectability of such embedded disks and concluded that disks contributing up to 20% of the light would remain undetectable in half of all ellipticals because of low inclinations. Kinematic studies demonstrated that, like S0 galaxies, disky ellipticals are in general rapid rotators (Bender 1988; Scorza & Bender 1995). Further similarities were found to exist in the radio and X-ray properties (Bender et al. 1989a; Eskridge et al. 1995) and in the way that objects populate the Fundamental Plane (Capaccioli et al. 1992).

In order to investigate more quantitatively the disk hypothesis and the family likeness between disky Es and S0 galaxies, it is necessary to study a significant number of objects and analyse their properties in great detail. Work on a few objects has been already done (Capaccioli et al. 1987; Scorza & Bender 1990; Simien & Michard 1990; Rix & White 1990, 1992; Scorza 1992; Cinzano & van der Marel 1994; Iodice et al. 1997). Scorza & Bender (1995) developed a method which allowed to decompose photometrically 12 disky ellipticals in their disk and bulge components, making possible the direct comparison between the decomposed components of Es and S0 galaxies. They showed that not only the detailed photometric structure of disky ellipticals can be understood in terms of disk+bulge models, but also their detailed kinematic properties. Indeed, the velocity line profiles (VLPs) of disky ellipticals show the same kind of asymmetries found in S0 galaxies (e.g. NGC 3115 in Scorza & Bender 1995), making the most plausible explanation that of the presence of an embedded disk.

In the present work we apply a similar technique as Scorza & Bender's (1995) with the aim of analysing a larger sample of early-type galaxies and re-examine the validity of the previous findings. With an improved method we are able to recover disks with arbitrary surface brightness profiles. In a forthcoming paper (Scorza & Bender 1998) we present a statistical study of disky ellipticals and S0 properties and give insights about the continuity of the Hubble sequence towards smaller D/B ratios.

The present paper is structured as follows. The observations, reduction procedure and isophote analysis are described in Sect. 2. A Morphological characterization of the studied objects is presented in Sect. 3. The decomposition method is introduced in Sect. 4 together with details of the calibration of the images and determination of characteristic parameters. In Sect. 5 we discuss the results of the decomposition, compare our results with previous work and discuss in detail some individual cases. The conclusions and final discussion are drawn in Sect. 6.