Excitation of the Infrared Lines of Fe XIII in the Solar Corona

The intensity ratios of X1O747 and X1O798 are calculated for an eighteen-level model ion having the 3s23p', 3s3p3, 3s23p3d states. The collision strength, (3p0,3p1) is close to 0.03 as indicated by a cornparison with observed ratios. The abundance of iron relative to hydrogen appears to be approximately 6>c l( in the corona as determined from observed line to continuum ratios of 1O747. The per cent linear polarization of the infrared lines in a coronal streamer is estimated taking collisional excitation into account.