The magnitudes and diameters are two of the fundamental parameters defining the equilibrium status of galaxies. This is particularly well illustrated by the formalism of the Fundamental Plane of early type galaxies (Dressler et al. 1987; Djorgovski & Davis 1987), where the total magnitude and effective radius scale the mass and the gravitational energy while the central velocity dispersion scales the kinetic energy, both being linked by the virial theorem. In addition, colours and colour gradients characterize the stellar populations (mean age and metallicity) and the amount and distribution of absorbing material. Also, the shape of the photometric profile (or of the growth curve) enters the scaling relations (Prugniel & Simien 1997).
Since the beginning of the photometry of galaxies (Whitford 1936) the bulk of photometric data available has increased exponentially (Prugniel 1987). However, these data are inhomogeneous both in their quality and form: They are based on photoelectric, photographic or CCD observations, and they are presented as centered aperture photometry through circular or elliptical apertures or as photometric profiles. The largest effort for deriving the fundamental parameters on a whole-sky homogeneous form was part of the production of the Third Reference Catalogue (RC3) (de Vaucouleurs et al. 1991; Buta et al. 1995; Buta & Williams 1995). The principle was to use a catalogue of photoelectric photometry (an update of the catalogues of aperture photometry by Longo & de Vaucouleurs 1983, 1985, 1988) to fit curves of growth and to derive magnitudes, diameters and colours. Each individual original reference from these catalogue was analysed, corrected for systematic effects and affected a weight.
In order to take into account the continuously growing amount of of photometric data on galaxies, we have written a non-interactive growth curve fitting algorithm to derive magnitudes, radii, colour and colour gradients and photometric type (ie. shape of the growth curve).
Our photometric database consists in: (1) an update of the Longo & de Vaucouleurs catalogues of photoelectric aperture photometry, (2) the photographic aperture photometry listed in the computerized version of the ESO-LV catalogue (Lauberts & Valentjin 1989, hereafter ESO-LV, (3) aperture photometry derived from published photometric profiles, mostly from CCD observations (in particular the I-band photometry by Mathewson et al. 1992), and (4) CCD photometry obtained at the 1.2 m telescope of the Observatoire de Haute-Provence. Using this database we already derived the photometric parameters used in Prugniel et al. (1993) and Prugniel & Simien (1994-1997).
In this paper we present our database (Sect. 2) and the fitting method and homogenisation (Sect. 3). The shape of growth curves is analysed in Sect. 4 and the derived parameters and comparison with RC3 are presented in Sect. 5. We discuss the physical meaning of the photometric type in Sect. 6.