The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields

III. Theoretical spectral patterns in the Paschen-Back regime

¹ Institut für Astronomie, ETHZ, 8092 Zürich, Switzerland e-mail: sveta@astro.phys.ethz.ch
² Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
³ Institute of Physics, St.-Petersburg University, Russia
⁴ Max-Planck-Institut für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany

Received: 10 July 2005
Accepted: 20 October 2005

Abstract

Many diatomic molecules present in the atmospheres of the Sun and cool stars exhibit the Paschen-Back effect at field strengths typical of sunspots and active cool stars. Here we present a complete theoretical description of the molecular Paschen-Back efect in Hund's cases (a), (b) and all cases intermediate to them. This description allows us to compute the splitting of levels of any multiplicity and the transitions between them. We also introduce a generalized description of the effective magnetic Landé factor applicable not just in the Zeeman regime, but also in the Paschen-Back regime. We find that in the regime of the partial Paschen-Back effect strongly asymmetric Stokes profiles are produced, whose strengths and asymmetries depend sensitively on the magnetic field. In the regime of the complete Paschen-Back effect the profiles become symmetric again (although they may be strongly shifted). The strength of the forbidden and satellite transitions increases rapidly with field strength in the partial Paschen-Back regime, while the strength of the main branch transitions decreases. These signatures hold promise to form the basis of new diagnostics of solar and stellar magnetic fields.