Spatially resolved spectroscopy across stellar surfaces

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.
17 pages, 10 figures, accepted for publication in Astronomy & Astrophysics