Interpreting Recent Observations of He I 10830 Å

Abstract

Spectra-spectroheliograms obtained in the 10830 Å line with the NASA/NSO Spectromagnetograph are analyzed to produce images in equivalent width, line depth, velocity, and continuum intensity. These and other images imply that if large-scale deficits in coronal irradiation induce weakening of the 10830 line, the ionizing radiation must be produced in close enough spatial proximity to the region of formation for 10830 to allow sharply defined spatial boundaries. The complex morphology of the images shows the importance of underlying chromospheric structure in providing a highly variable “substrate” which is modulated by varying illumination. Clear evidence is seen of He I 10830 Å formation in magnetic loops where the velocity field, particularly at footpoints, directly affects the excitation of the line. Steady flows as seen by Lites et al. (1985) are also observed, particularly near the limb. The observations and radiative transfer calculations are consistent with a simple, optically thin “cloud” model of line formation, and observed line profiles in weak network elements compare favorably with predictions from mean models.