FeH and its capability to measure magnetic fields on M dwarfs

• Main Authors: Afram, N, Reiners, A, Berdyugina, S V
• Format: Conference Proceeding
• Language: English
• ISSN: 0094-243X
• DOI: 10.1063/1.3099211

Iron hydride (FeH) bands are the most sensitive indicators of magnetic fields in cool atmospheres, where atomic lines lose their utility. In the first part of our work, we established the theoretical foundations for the analysis of the astrophysically important Wing-Ford FeH F4D-X4D system around 1 mum. We calculated the molecular Zeeman effect, computed the Lande factors of the energy levels and transitions, and calibrated molecular constants to account for unknown perturbations by comparing observed and modeled sunspot spectra. In the second part we illustrate the applicability of the FeH lines to diagnose stellar magnetic fields. We modeled highly magnetically sensitive FeH line profiles employing our novel quantum-mechanical treatment of the Zeeman effect in the FeH molecule and compared them with observed M dwarf spectra to infer magnetic field strengths. Measurements of magnetic fields on cool M dwarfs provide important information on stellar dynamo processes, since the transformation between the solar type to a turbulent dynamo takes place roughly at a spectral type M3 to M4 and the dynamo mechanism that generates and amplifies magnetic fields in fully convective stars is still unknown.