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Astronomy & Astrophysics manuscript no. 3099 May 11, 2005 (DOI: will be inserted by hand later)

Summary: Astronomy & Astrophysics manuscript no. 3099 May 11, 2005
(DOI: will be inserted by hand later)
Evidence for Explosive Event Activity Originating in the
J.G. Doyle 1 , B. Ishak 1 , I. Ugarte­Urra 1# , P. Bryans 2 , and H.P. Summers 2
1 Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
2 Department of Physics, University of Strathclyde, Glasgow, Scotland
the date of receipt and acceptance should be inserted later
Abstract. We report on a joint SUMER, CDS, TRACE study, concentrating on a region which shows prolonged
EUV explosive event (EE) activity in the transition region line N v 1238 š A, yet little evidence of such activity in
another transition region line O v 629 š A (formed at a similar temperature) which was observed simultaneously.
A possible explanation for the lack of major activity in the O v line in several explosive events could be that
they originate in the lower chromosphere. This is consistent with the enhancements in the C i 1249 š A line and
with the findings of another study which reported time delays between the chromospheric and transition region
lines in some EE's using high cadence observations (10 s exposure time) obtained with the SUMER spectrometer
in H i Ly 6 (20 000 K) and S vi (200 000 K). Using the generalized collisional­radiative picture, including the
population of metastable levels, we derive the density dependent contribution function for both N v 1238 and
O v 629 for four values of the electron density; 10 6 cm -3 representing the low density limit, 10 9 cm -3 for a typical
quiet Sun electron density plus 10 11 cm -3 and 10 12 cm -3 for an active region. These calculations show that with
increasing electron density, both lines shift to slightly lower temperatures. However, the major di#erence is in the


Source: Armagh Observatory


Collections: Physics