Context :

Aims : We present a coherent stellar and nebular model that reproduces observations of the planetary nebula IC418 .
We aim to test whether a stellar model found to provide an optimal description of the stellar observations is able to satisfactory ionize the nebula and reproduce the nebular observations , a finding that is by no mean evident .
This allows us to determine all the physical parameters of both the star and the nebula , including chemical abundances and the distance .

Methods : We used all the observational material available ( FUSE , IUE , STIS and optical spectra ) to constrain the stellar atmosphere model performed using the CMFGEN code .
The photoionization model is developed by comparing solutions provides by Cloudy_3D , with results from CTIO , Lick , SPM , IUE , and ISO spectra as well as HST images .
The aperture sizes and positions of the different observations are taken into account .
More than 140 model nebular emission lines are compared to the observed intensities .
The distance is determined using evolutionary tracks .

Results : We reproduce all the observations for the star and the nebula .
The 3D morphology of the gas distribution is determined .
The effective temperature of the star is 36.7 \pm 0.5 kK .
Its luminosity is 7700 L _ { \odot } .
No clumping factor is needed to reproduce the age-luminosity relation .
We describe an original method for determining the distance of the nebula using evolutionary tracks .
The distance of 1.25 kpc is found to be in very good agreement with recent determination using parallax method , and the age of the nebula is estimated to be 1400 years .
The chemical composition of both the star and the nebula are determined .
Both are carbon-rich .
The nebula exhibits evidence of the depletion of elements Mg , Si , S , Cl ( 0.5 dex lower than solar ) , and Fe ( 2.9 dex lower than solar ) , which is indicative of a depletion of these elements onto grains .

Conclusions : We develop the first self-consistent stellar and nebular model of a planetary nebula that reproduces all the available observations ranging from IR to UV , showing that the combined approach to the modeling process leads to more restrictive constraints and , in principle , more trustworthy results .