HAO Colloquium - Gabriel Dima, HAO

Solving the puzzle of faint neutral helium emission in the solar corona

Tracing the abundance of helium and its variation from the solar interior to its atmosphere, through the solar wind, and into the inner heliosphere is essential to understanding the energetics of the heliosphere and requires a major observational undertaking, now embodied in the multi-messenger era by DKIST, Parker Solar Probe, and Solar Orbiter. Recent sounding rocket observations have shown that the morphology of the He corona is different from the morphology of the H corona due to significant variations in helium abundance. The few ground-based detections of coronal HeI 1083 nm emission in the infrared have found line brightness values ~5x10^-7 Idisc and line widths consistent with chromospheric temperatures. These brightness values are nearly an order of magnitude lower than other coronal emission lines and follow-up observations have proved challenging to achieve from the ground outside eclipse conditions. Recent work on collisional radiative models, including dielectronic recombination, predicts comparable emissivities for the HeI 1083 nm and Fe XIII 1079 nm lines at lower coronal densities and temperatures but predict much wider line widths than observed to date. Because the HeI 1083 nm is sensitive to the magnetic field strength in the 0.1-8 G range through the Hanle effect it may prove a useful probe of coronal magnetic fields in weaker regions where measuring circular polarization due to the Zeeman effect would be very challenging. In this talk I will review the current understanding on the faint neutral helium emission from the solar corona and discuss upcoming high sensitivity DKIST observations that will shine new light on the origin of the signal. 


Date and time: 
Wednesday, May 19, 2021 - 2:00pm to 3:00pm