Context : Isolated early-type galaxies are evolving in unusually poor environments for this morphological family , which is typical of cluster inhabitants .
We investigate the mechanisms driving the evolution of these galaxies .

Aims : Several studies indicate that interactions , accretions , and merging episodes leave their signature on the galaxy structure , from the nucleus down to the faint outskirts .
We focus on revealing such signatures , if any , in a sample of isolated early-type galaxies , and we quantitatively revise their galaxy classification .

Methods : We observed 20 ( out of 104 ) isolated early-type galaxies , selected from the AMIGA catalog , with the 4KCCD camera at the Vatican Advanced Technology Telescope ( VATT ) in the Sloan Digital Sky Survey ( SDSS ) g and r bands .
These are the deepest observations of a sample of isolated early-type galaxies so far : on average , the light profiles reach \mu _ { g } \approx 28.11 \pm 0.70 mag arcsec ^ { -2 } and \mu _ { r } \approx 27.36 \pm 0.68 mag arcsec ^ { -2 } .
The analysis was performed using the AIDA package , providing point spread function-corrected 2D surface photometry up to the galaxy outskirts .
The package provides a model of the 2D galaxy light distribution , which after model subtraction enhances the fine and peculiar structures in the residual image of the galaxies .

Results : Our re-classification suggests that the sample is composed of bona fide early-type galaxies spanning from ellipticals to late-S0s galaxies .
Most of the surface brightness profiles are best fitted with a bulge plus disc model , suggesting the presence of an underlying disc structure .
The residuals obtained after the model subtraction show the nearly ubiquitous presence of fine structures , such as shells , stellar fans , rings , and tails .
Shell systems are revealed in about 60 % of these galaxies .

Conclusions : Because interaction , accretion , and merging events are widely interpreted as the origin of the fans , ripples , shells and tails in galaxies , we suggest that most of these isolated early-type galaxies have experienced such events .
Because they are isolated ( after 2-3 Gyr ) , these galaxies are the cleanest environment in which to study phenomena connected with events like these .