EDP Sciences
Free access
Issue
A&A
Volume 392, Number 1, September II 2002
Page(s) 309 - 317
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20020795


A&A 392, 309-317 (2002)
DOI: 10.1051/0004-6361:20020795

Transition region explosive events: Do they have a coronal counterpart?

L. Teriaca1, M. S. Madjarska2 and J. G. Doyle2

1  Osservatorio Astrofisico di Arcetri, 50125 Firenze, Italy
2  Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland

(Received 22 February (2002) / Accepted 27 May (2002) )

Abstract
EUV explosive events are a prominent class of phenomena characterizing the solar transition region. Their correct location in the wider frame-work of the outer solar atmosphere can provide important insight on the nature of the transition region itself and its relationship with the hotter corona and the cooler chromosphere. In this paper we present new high-cadence SUMER observations of the "quiet" Sun obtained simultaneously in the mid-transition region N V 1238.8 Å line ( $1.8\times 10^{5}$ K) and in the coronal Mg X 625 Å line ( $1.1\times 10^{6}$ K). These observations are aimed at providing information on the behaviour of the coronal plasma during EUV transition region explosive events detected in N V 1238.8 Å. None of the events observed in N V shows any detectable signature in the Mg X line profile or in its integrated intensity. The analysis of 1996 observations obtained simultaneously in N V 1238.8 Å and S II 1253.8 Å ( $3.5\times 10^{4}$ K) shows, instead, a weak but clear presence of enhanced wings in the S II line profile during a series of events observed in N V. These results suggest that EUV explosive events are not directly relevant in heating the corona and are characteristic of structures not obviously connected with the upper corona. The evidence of a chromospheric response suggests that, contrary to some previous suggestions, explosive events have a chromospheric origin.


Key words: Sun: transition region, explosive events, corona -- UV radiation

Offprint request: L. Teriaca, lte@arcetri.astro.it
or http://star.arm.ac.uk/preprints/




© ESO 2002

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