Measurement of the photoionization cross section of neutral iron

Abstract

The photoionization cross section of neutral iron, in thermal equilibrium 2300 K, was measured to be (${5.0}_{\ensuremath{-}0.7}^{+0.4}$) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}18}$ ${\mathrm{cm}}^{2}$ at 1540 \AA{} (8.05 eV). At this temperature more than 98% of the atoms are in the levels of the ground term. The iron vapor was produced in a resistively heated furnace, and the column density was determined by the hook method. The optical depth of the iron vapor was measured with a photoelectric detector. The absolute measurement of the cross section can be used to calibrate existing data which cover a wide range of wavelengths.