1 Introduction

The shape of the surface brightness profiles of elliptical galaxies, quantified by the parameter N in the Sérsic (1968) law

$$I_{(r)} = I_0 \,{\rm e}^{-(r/\alpha)^N} ,$$ (1)

has been shown to correlate with luminosity, both for dwarf (Young & Currie 1994, hereafter YC94; Cellone et al. 1994; Durrell et al. 1996; Durrell 1997) and bright systems (Caon et al. 1993; D'Onofrio et al. 1994).

The use of this L-N relationship as a distance indicator for dwarf elliptical galaxies was first investigated by YC94, while the correlation between the Sérsic parameters N and $\alpha$ was subsequently used (Young & Currie 1995, YC95) to derive the distances to 64 dwarf galaxies in the Virgo Cluster. The quest about the real usefulness of the L-N and $\alpha-N$ relations to determine extragalactic distances has received opposite arguments in favour (Young & Currie 1998) or against (Binggeli & Jerjen 1998, BJ98).

In a recent paper, Cellone (1999, C99) presented CCD surface photometry for a small sample of dwarf and intermediate luminosity galaxies in the NGC5044 Group, showing that, at least in that case, the L-N correlation partially fails due to a few relatively bright galaxies with "convex'' profiles (i.e. N>1) strongly deviating from the standard relationship. In addition, the important intrinsic scatter in the L vs. N trend seems to drastically limit its practical use for obtaining the distance to the group.

A re-elaboration of a subset of those data, led Young & Currie (2001, YC00) to conclude that the galaxy population in the NGC5044 Group displays on the contrary "a tight scalelength-shape relationship'' revealing therefore to be "an excellent distance indicator''.

As we will show in the present paper, there are reasons to believe that most of the YC00 conclusions rest in fact on a misinterpretation of the data (Sect. 2), while their claimed apparent tightness of the $\alpha-N$ relation seems likely an artifact of the parameter mathematical coupling in Eq. (1). This would therefore throw serious doubts in using this method to derive extragalactic distances (Sect. 4.1).

We will also turn back here to the relevant case of galaxy N50 in the NGC5044 Group, one of those "outliers'' escaping the standard L-Nrelation in Cellone's (1999) analysis. In spite of its ostensibly normal dE photometric properties, new accurate observations (Sect. 3) indicate indeed that this is a quite peculiar and interesting object sharing most of the characters of dwarf ellipticals (dE) and blue compact dwarf (BCD) galaxies.