  High-precision stellar analyses require hydrodynamic 3D modeling. Such models
predict changes across stellar disks of spectral line shapes, asymmetries, and
wavelength shifts. For testing models in stars other than the Sun, spatially
resolved observations are feasible from differential spectroscopy during
exoplanet transits, retrieving spectra of stellar surface segments that
successively become hidden behind the transiting planet, as shown in Papers I,
II, and III. Synthetic high-resolution spectra over extended spectral regions
are now available from 3D models. Similar to other ab initio simulations, these
data contain patterns that have not been specifically modeled but may be
revealed after analyses analogous to those of a large volume of observations.
From five 3D models spanning T=3964-6726K (approx. spectral types K8V-F3V),
synthetic spectra at hyper-high resolution (R>1,000,000) were analyzed.
Selected FeI and FeII lines at various positions across stellar disks were
searched for patterns between different lines in the same star and for similar
lines between different stars. Such patterns are identified for representative
photospheric lines of different strengths, excitation potential, and ionization
level, encoding the hydrodynamic 3D structure. Line profiles and bisectors are
shown for various stars at different positions across stellar disks. Absolute
convective wavelength shifts are obtained as differences to 1D models, where
such shifts do not occur. Observable relationships for line properties are
retrieved from realistically complex synthetic spectra. Such patterns may also
test very detailed 3D modeling, including non-LTE effects. While present
results are obtained at hyper-high spectral resolution, the subsequent Paper V
examines their practical observability at realistically lower resolutions, and
in the presence of noise.
