DETECTION OF POLARIZATION FROM THE E ~4II-A ~4II SYSTEM OF FeH IN SUNSPOT SPECTRA

摘要

Here we report the first detection of polarization signals induced by the Zeeman effect in spectral lines of the E ~4II_A ~4II system of FeH located around 1.6 μm. Motivated by the tentative detection of this band in the intensity spectrum of late-type dwarfs, we have investigated the full Stokes sunspot spectrum and have found circular and linear polarization signatures that we associate with the FeH lines of the E ~4II-A ~4II band system. We investigate the Zeeman effect in these molecular transitions and point out that in Hund's case (a) coupling, the effective Lande factors are never negative. For this reason, the fact that our spectropolarimetric observations indicate that the Lande factors of pairs of FeH lines have opposite signs prompts us to conclude that the E ~4II-A ~4II system must be in intermediate angular momentum coupling between Hund's cases (a) and (b). We emphasize that theoretical and/or laboratory investigations of this molecular system are urgently needed for exploiting its promising diagnostic capabilities.