2 Observations, reduction and isophote analysis

Twenty-five of the 28 early-type galaxies studied here are part of the ESO key-project sample "Towards a physical classification of early-type galaxies'' (Bender et al. 1989b). They were observed at the 1.5 m Danish and the MPI 2.2 m telescopes of La Silla, Chile. These galaxies are listed in the RC2 catalogue (de Vaucouleurs et al. 1976) and LV catalogue (Lauberts & Valentijn 1989) with types T< -3 and are brighter than $B_{\rm t} = 13.5$ mag. The detector was an RCA CCD with a pixel size of $15~\mu$m, which yielded a resolution of 0.23 arcsec pro pixel. The exposure times were typically of 20 to 30 minutes in the V filter and 7 to 20 minutes in the R filter.

NGC 4473, NGC  4550 and NGC 4564 were observed at the 1.23 m telescope of the German-Spanish Astronomical center, Calar Alto, Spain. The detector was a GEC CCD with a pixel size of $22~\mu$, which yielded a resolution of 0.46 arsec pro pixel in a field of $3\times 4$ arcmin.

Along the observations the seeing had in average a value of 2 arcsec. After standard reduction (dark subtraction, flatfield division), the galaxies isophotes were analysed following Bender & Möllenhoff (1987). This provided the parameters of the best fitting ellipses and the Fourier-coefficients measuring the deviations of the isophotes from ellipses.

The sample was chosen primarily according to the amplitude of the a₄/a*100 Fourier coefficient, which has proven to be a very good indicator for the existence of embedded disks (see references above). The sample is a semi-random subset of all objects with positive a₄/a*100. However objects with large isophote twists and objects with significant dust absorption were excluded. Table 1 lists the 28 early-type galaxies analysed here, their morphological types and $B_{\rm T}$ magnitudes according the RC3 catalogue (de Vaucouleurs et al. 1991), the morphological types according to our analysis (Type SB98, see below), the maximum values of the a₄/a*100 Fourier coefficient, the filter in which the images were obtained and the galactic standard of rest radial velocities ($V_{\rm gsr}$) in km s^-1 taken from the RC3 catalogue.

  

Table 1: Basic parameters of the observed galaxies. For each object, we list the classification and $B_{\rm T}$ according to the RC3, the morphological classification according to our analysis (Type SB98), the maximum values of the a₄/a*100 Fourier coefficient, the filter in which the images were taken and the radial velocities corrected to the galactic center $V_{\rm gsr}$ from the RC3 catalogue