LABORATORY MEASUREMENTS OF THE ZEEMAN EFFECT IN THE F--X SYSTEM OF IRON MONOHYDRIDE

Abstract

We have used a hollow cathode sputtering source, flowing a mixture of 10~\% H$_2$ in Ar $\sim$ 45 standard cm$^3$/minute to form FeH radicals. Sputtering from iron required currents $\geq$ 250 mA. A permanent magnet was placed 2--3 cm below the cathode, generating magnetic fields 3000--4500 Gauss. Output from a Sirah Matisse Ti:sapphire laser was focused to a beamwaist $<$ 1mm to probe a reasonably homogeneous region of the magnetic field, with the laser operating around 1 $\mu$m for the 0-0 band and 890 nm for the 1-0 band of the $\emph{F}~^4\Delta$Ê$\leftarrow\emph{X}~^4\Delta$ system in FeH. The magnetic field is calibrated to 0.5 \% accuracy from the Zeeman response of the Ar I line at 10958.339 cm$^{-1}$. Several spectra have been taken for lines of the R branches of the $\emph{F}~^4\Delta_{7/2}\leftarrow\emph{X}~^4\Delta_{7/2}$ and $\emph{F}~^4\Delta_{5/2}\leftarrow\emph{X}~^4\Delta_{5/2}$ sub-bands, showing resolved structures at Doppler resolutions. Unresolved structures are seen for the Q and P transitions. Lande factors have been determined for the upper state (relying on ground state data from LMR work 234309 (2006)) either from fits to peak positions, or by simulating observed profiles when this was impossible. The Lande factors have been used to deduce a magnetic field of 2200 Gauss in sunspots from lines near 1 $\mu$m observed at the solar telescope THEMIS (Tenerife) in July 2011. Stokes V profiles were recorded at the telescope, for optimum sensitivity. The magnetic field deduced from atomic lines (Ti,Fe) is around 10~\% higher than that found from FeH, compatible with molecules forming at higher altitudes in the solar atmosphere.