EDP Sciences
Free access
Volume 401, Number 3, April III 2003
Page(s) 1131 - 1142
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20021891

A&A 401, 1131-1142 (2003)
DOI: 10.1051/0004-6361:20021891

A transient event in lines of Ne V, VI and VII

E. R. Houdebine and C. Jordan

Department of Physics (Theoretical Physics), Oxford University, 1 Keble Road, Oxford OX1 3NP, UK
    e-mail: erh@thphys.ox.ac.uk; cj@thphys.ox.ac.uk
(Received 18 September 2002 / Accepted 20 December 2002 )

We report observations of a transition region brightening made with the Coronal Diagnostic Spectrometer onboard the Solar and Heliospheric Observatory. We observed a region of the quiet Sun in 12 spectral lines with temperatures of formation from $\simeq$ $3 \times
10^4$  K to $1.1 \times 10^6$ K. The transient event occured in a network boundary region and was most pronounced in the Ne VI 562.8-Å line. Although the Ne V 572.3-Å and Ne VII 561.7-Å lines also show increases in intensity, the changes in the lines of helium, oxygen and magnesium, formed at lower or higher temperatures, are smaller or not significant. Thus the event is most significant in the relatively narrow temperature range of $\simeq$ $3 \times 10^5$ K to $\simeq$ $5 \times 10^5$ K. The event lasted at least 53 min. In the many data sets we have obtained, only one other region shows an obviously high Ne VI to O IV intensity ratio, so the observed event is clearly unusual. Previous studies of blinkers have not included the lines of Ne V, Ne VI or Ne VII; the highest temperature transition region line used has been the O V 627.9-Å line. Future studies of blinkers should include these higher temperature lines. We derive volume emission measures in the event from the various line intensities, estimate the electron densities and discuss the energy budget and possible origins of the event.

Key words: Sun: transition region -- Sun: activity -- Sun: UV radiation

Offprint request: E. R. Houdebine, erh@thphys.ox.ac.uk

© ESO 2003