Signatures of transition region explosive events in hydrogen Lyβ profiles

¹ CAS Key Laboratory of Basic Plasma Physics, School of Earth and Space Sciences, Univ. of Science and Technology of China, Hefei, Anhui, PR China e-mail: xld@sdu.edu.cn
² Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Shandong Univ. at Weihai, Weihai, Shandong, PR China
³ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
⁴ School of Earth and Space Sciences, Peking University, PR China

Received: 11 February 2010
Accepted: 10 May 2010

Abstract

Aims. We search for signatures of transition region explosive events (EEs) in hydrogen Lyβ profiles. The relationship between the peak emission of Lyβ profiles and the wing emission of C ii and O vi during EEs is investigated.

Methods. Two rasters made by the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) instrument onboard SOHO in a quiet-Sun region and an equatorial coronal hole were selected for our study. Transition-region explosive events were identified from profiles of C ii 1037  Å and O vi 1032  Å, respectively. We compared Lyβ profiles during EEs with those averaged in the entire quiet-Sun and coronal-hole regions.

Results. We find that the central part of Lyβ profiles reverses more and the distance of the two peaks becomes larger during EEs, both in the coronal hole and in the quiet Sun. The average Lyβ profile of the EEs detected by C ii has an obviously stronger blue peak. During EEs, there is a clear correlation between the increased peak emission of Lyβ profiles and the enhanced wing emission of the C ii and O vi lines. The correlation is more pronounced for the Lyβ peaks and C ii wings, and less significant for the Lyβ blue peak and O vi blue wing. We also find that the Lyβ profiles are more reversed in the coronal hole than in the quiet Sun.

Conclusions. We suggest that the jets produced by EEs emit the Doppler-shifted Lyβ photons, causing enhanced emission at positions of the peaks of Lyβ profiles. The more-reversed Lyβ profiles confirm the presence of higher opacity in the coronal hole than in the quiet Sun. The finding that EEs modify the Lyβ line profile in QS and CHs implies that one should be careful in the modeling and interpretation of relevant observational data.