SUMER-Hinode observations of microflares: excitation of molecular hydrogen

TL;DR

This study uses SUMER and Hinode observations to show that microflares heat the chromosphere, enabling O VI emission to excite molecular hydrogen, revealing new insights into microflare energy dissipation.

Contribution

It provides the first coordinated observations linking microflare activity with H2 excitation and chromospheric heating mechanisms.

Findings

H2 excitation occurs near brightening X-ray loop footpoints.

Microflare energy heats the chromosphere, reducing opacity.

H2 events are associated with specific plasma outflows.

Abstract

Concentrations of molecular hydrogen (H2) have been detected by SUMER in active region plage. The H2 is excited by O VI line emission at 1031.94 A which, although not observed, must be brightening along with the observed transition region line, Si III 1113.24 A. We have made co-ordinated observations of active region plage with the spectrometer SUMER/SoHO in lines of H2 1119.10 A and Si III 1113.24 A and with XRT/Hinode X-ray and SOT/Hinode Ca II filters. In six hours of observation, six of the seven H2 events seen occurred near a footpoint of a brightening X-ray loop. The seventh is associated with an unusually strong Si III plasma outflow. We conclude that microflare energy dissipation heats the chromosphere, reducing its opacity, so that O VI microflare emission is able to reach the lower layers of the chromosphere and excite the H2.