Letter to the Editor

SUMER-Hinode observations of microflares: excitation of molecular hydrogen

Max-Planck Institut für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany e-mail: innes@mps.mpg.de

Received: 1 November 2007
Accepted: 20 November 2007

Abstract

Context.Concentrations of H₂ have been detected by SUMER in active region plage. The H₂ is excited by O  line emission at 1031.94 Å which, although not observed, must be brightening along with the observed transition region line,  1113.24 Å.

Aims.We investigate the excitation of H₂ and demonstrate the association between the observed H₂ emission and footpoints of X-ray microflares.

Methods.We have made co-ordinated observations of active region plage with the spectrometer SUMER/SoHO in lines of H₂ 1119.10 Å and  1113.24 Å and with XRT/Hinode X-ray and SOT/Hinode Ca  filters.

Results.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  plasma outflow.

Conclusions.Microflare energy dissipation heats the chromosphere, reducing its opacity, so that O  microflare emission is able to reach the lower layers of the chromosphere and excite the H₂.