  The importance of magnetic fields in three-dimensional magnetoconvection
models of the Sun's photosphere is investigated in terms of their influence on
the continuum intensity at different viewing inclination angles, and on the
intensity profile of two [O I] spectral lines. We use the RH numerical
radiative transfer code to perform a posteriori spectral synthesis on the same
time-series of magnetoconvection models used in our publications on the effect
of magnetic fields on abundance determination. We obtain a good match of the
synthetic disc-centre continuum intensity to the absolute continuum values from
the FTS observational spectrum; the match of the centre-to-limb variation (CLV)
synthetic data to observations is also good, thanks, in part, to the 3D
radiation transfer capabilities of the RH code. The different levels of
magnetic flux in the numerical time-series do not modify the quality of the
match. Concerning the targetted [O I] spectral lines, we find, instead, that
magnetic fields lead to non-negligible changes in the synthetic spectrum, with
larger average magnetic flux causing the line to become noticeably weaker. The
photospheric oxygen abundance that one would derive if instead using
non-magnetic numerical models would thus be lower by a few to several
centidexes. The inclusion of magnetic fields is confirmed to be important for
improving the current modelling of the Sun, here in particular in terms of
spectral line formation and of deriving consistent chemical abundances. These
results may shed further light on the still controversial issue regarding the
precise value of the solar oxygen abundance.
