Luminosity index: lambda
The luminosity index lambda is calculated according to
de Vaucouleurs et al. (1979), using the luminosity class
lc and morphological type t codes:
lambda = (lcc + t)/10
where lcc is the luminosity class corrected for inclination according to
the relation
lcc = lc - (c . logr25)
where logr25 is the axis ratio and c
is a parameter depending on the morphological type t
(c = 2.0 for t <=5 and c = 2.0 -0.9(t-5), otherwise)