Afram, N: Molecular Diagnostics of Solar and Stellar Magneti

magnetic field strengths in different astrophysical objects, such as M dwarfs. On cool stars, atomic lines vanish among the dominating presence of molecular features, and thus, it is of advantage to utilize molecular lines instead. The study of M dwarfs is of special interest, because the transition from stars with an outer convection zone to fully convective stars takes place. In the latter, the solar type dynamo must be replaced by an alternative mechanism, such as a turbulent dynamo, to amplify magnetic fields. With the previous development of the FeH F4?-X4? system into a diagnostic tool, we determine magnetic fields on a sample of M stars through a comparison of synthetic and observed spectral lines, which are especially magnetically sensitive. Our study is then extended to the analysis of the usefulness of various molecules, FeH, MgH, TiO, and CaH, as diagnostics for exploring stellar magnetism on active G-K-M stars. We present the temperature range in which the selected molecules can serve as indicators for magnetic fields on highly active cool stars. In particular, the detection of circular polarization in MgH and FeH lines on M dwarfs is shown and supports the predictions of our modeling. In the next step, we utilize the successful direct modeling of MgH and TiO lines in sunspots as a starting point for inversions, i.e. the determination of the physical parameters of the sunspot atmosphere. Including both molecular and atomic lines in these preliminary inversions promises a dramatic improvement of the deduced atmosphere model. Molecular lines prove to be excellent diagnostics to provide information on solar and stellar magnetic fields. Advances in the constantly growing field of molecular spectroscopy and spectropolarimetry depend largely on the following criteria: On one hand, from a theoretical point of view, much work remains to be done for the mostly very complicated cases of the molecular Zeeman and Paschen-Back effects. On the other hand, improved observational instrumentation at the new generation of large telescopes, such as highly sensitive spectropolarimeters, are designed to measure with high precision the polarization state of the received photons and may reveal new polarization phenomena in molecules.